Preventing other applications from binding to port 80 and 443

You can't prevent a port from being bound by the wrong service. In your case, just remove apache from autostart and you should be good.

For 16.04 and newer:

sudo systemctl disable apache2

For older Ubuntu versions:

sudo update-rc.d apache2 disable

If you really aren't using apache2, and it's PHP 7.0 that's requiring it, then it looks like you have libapache2-mod-php7.0 installed. That package is useless without Apache. Since you're using nginx, you likely also have php7.0-fpm or php7.0-cgi installed, either of which is sufficient for satisfying php7.0's dependency requirements:

$ apt-cache depends php7.0
php7.0
 |Depends: php7.0-fpm
 |Depends: libapache2-mod-php7.0
  Depends: php7.0-cgi
  Depends: php7.0-common
  Conflicts: <php5>

If you do have either of php7.0-{fpm,cgi} installed, you can go ahead and uninstall Apache.