How do I remove a repository from the terminal?

You would need to locate the specific lines in /etc/apt/sources.list

Open the sources file with some editor while using sudo, such as vim (I personally use nano, but you can use whatever you want):

sudo vim /etc/apt/sources.list

Locate the lines which contain the broken link, and remove them. Save the files, then run sudo apt-get update after you save the file and close out the editor. Your sources will be updated to work with the non-broken repositories.

Note that if the lines don't show up in /etc/apt/sources.list then they'll exist in other files in /etc/apt/sources.list.d/ in which case you'll have to go through the files in that directory and comment out the broken source definition there.

If you need to manage PPAs then this question is for you:

• How can PPAs be removed?