Cannot upgrade 19.04 to 19.10 because of held back packages: libsnmp30

When running update-manager to upgrade 19.04 to 19.10 I get this in the console:

Checking for a new Ubuntu release
Please install all available updates for your release before upgrading.

Trying do-release-upgrade:

$ do-release-upgrade 
Checking for a new Ubuntu release
Please install all available updates for your release before upgrading.

So trying upgrade:

$ sudo apt-get upgrade 
The following packages have been kept back:
  libsnmp30
0 upgraded, 0 newly installed, 0 to remove and 1 not upgraded.

In fact, it seems I cannot install anything:

$ sudo apt-get install emacs
Reading package lists... Done
Building dependency tree       
Reading state information... Done
You might want to run 'apt --fix-broken install' to correct these.
The following packages have unmet dependencies:
 libsnmp30 : Depends: libsensors5 (>= 1:3.5.0) but it is not going to be installed
E: Unmet dependencies. Try 'apt --fix-broken install' with no packages (or specify a solution).

Trying with --fix-broken:

$ sudo apt --fix-broken install
Correcting dependencies... failed.
The following packages have unmet dependencies:
 libsnmp30 : Depends: libsensors5 (>= 1:3.5.0) but it is not installed
E: Error, pkgProblemResolver::Resolve generated breaks, this may be caused by held packages.
E: Unable to correct dependencies

Anyway, libsnmp30 seems to be the culprit. Trying to install libsnmp30, I get this:

$ sudo apt-get install libsnmp30
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 libsnmp30 : Depends: libsensors5 (>= 1:3.5.0) but it is not going to be installed
E: Unable to correct problems, you have held broken packages.

Then trying libsensors5:

$ sudo apt-get install libsensors5    
The following packages have unmet dependencies:
 libsensors5 : Depends: libsensors-config but it is not going to be installed
E: Unable to correct problems, you have held broken packages.

Then trying libsensors-config, this is the result which looks scary enough:

$ sudo apt-get install libsensors-config
The following additional packages will be installed:
  policykit-1-gnome
Suggested packages:
  lm-sensors
The following packages will be REMOVED:
  apturl cheese chrome-gnome-shell colord default-jre deja-dup evolution-data-server gdm3 gir1.2-gst-plugins-base-1.0 gir1.2-mutter-2
  gir1.2-mutter-4 gir1.2-rb-3.0 gir1.2-totem-1.0 gnome-initial-setup gnome-online-accounts gnome-session-bin gnome-shell gnome-shell-extension-appindicator
  [ ... lots and lots of packages ... ]
The following NEW packages will be installed:
  libsensors-config policykit-1-gnome
0 upgraded, 2 newly installed, 120 to remove and 0 not upgraded.

Jikes!

More info:

$ apt-cache policy libsnmp30
libsnmp30:
  Installed: 5.7.3+dfsg-1.8ubuntu3.1
  Candidate: 5.7.3+dfsg-5ubuntu1.2
  Version table:
     5.7.3+dfsg-5ubuntu1.2 500
        500 http://se.archive.ubuntu.com/ubuntu disco-updates/main amd64 Packages
     5.7.3+dfsg-5ubuntu1 500
        500 http://se.archive.ubuntu.com/ubuntu disco/main amd64 Packages
 *** 5.7.3+dfsg-1.8ubuntu3.1 100
        100 /var/lib/dpkg/status

Libsensors info:

$ apt-cache policy libsensors5 libsensors-config
libsensors5:
  Installed: (none)
  Candidate: 1:3.5.0-3ubuntu1
  Version table:
     1:3.5.0-3ubuntu1 500
        500 http://se.archive.ubuntu.com/ubuntu disco/main amd64 Packages
libsensors-config:
  Installed: (none)
  Candidate: 1:3.5.0-3ubuntu1
  Version table:
     1:3.5.0-3ubuntu1 500
        500 http://se.archive.ubuntu.com/ubuntu disco/main amd64 Packages
        500 http://se.archive.ubuntu.com/ubuntu disco/main i386 Packages

Removing libsensors4:

$ sudo apt remove libsensors4
You might want to run 'apt --fix-broken install' to correct these.
The following packages have unmet dependencies:
 libgl1-mesa-dri : Depends: libsensors4 (>= 1:3.0.0) but it is not going to be installed
 libsensors-config : Conflicts: libsensors4:i386 but 1:3.4.0-4 is to be installed
E: Unmet dependencies. Try 'apt --fix-broken install' with no packages (or specify a solution).

Info about libgl1-mesa-dri:

$ apt-cache policy libgl1-mesa-dri
libgl1-mesa-dri:
  Installed: 19.3~git1908270730.e6eb44~oibaf~b
  Candidate: 19.3~git1908270730.e6eb44~oibaf~b
  Version table:
 *** 19.3~git1908270730.e6eb44~oibaf~b 100
        100 /var/lib/dpkg/status
     19.0.8-0ubuntu0~19.04.1 500
        500 http://se.archive.ubuntu.com/ubuntu disco-updates/main amd64 Packages
     19.0.2-1ubuntu1 500
        500 http://se.archive.ubuntu.com/ubuntu disco/main amd64 Packages

You had a ppa installed that got removed at some point (maybe on an earlier Ubuntu upgrade), but the packages installed from that ppa are still on your system, resulting in dependency problems.

From your apt outputs, it seems to be ppa:oibaf/graphics-drivers.

Try adding that same ppa again, it seems to be available for cosmic:

sudo add-apt-repository ppa:oibaf/graphics-drivers

Then run

sudo apt --fix-broken install

If that worked, you can remove that ppa and all its packages if you like using ppa-purge

sudo apt install ppa-purge
sudo ppa-purge ppa:oibaf/graphics-drivers

At the end I'd issue to clean unreferenced packages:

sudo apt autoremove