Add enca to libass/mpv dependencies
Fix enca install
Remove gettext and glib

This shit is just far too broken. Fuck GNU forever. I will not deal
with this horrible abomination.
mpv: Download font as packaging step
Add force-update steps to all Git packages

This is really dumb. Apparently ExternalProject does not handle
this properly by default, and it executes custom update commands
only once. So we need to 1) override the default update command
and 2) add our own update step.