This gets rid of all those internal mounts, such as /snap mounts.
The approach is similar to GVFS which ignores everything outside /media, /home/user, and /media/run, cf. https://github.com/GNOME/gvfs/blob/master/monitor/udisks2/what-is-shown.txt
Explicitly creating a mount in /etc/fstab outside of those directories is still possible and will always show up.
BUG: 379516
CCBUG: 319998