Purge missing (new) ubuntustudio packages

See merge request trisquel/ubuntu-purge!40

ubuntustudio-live and ubuntustudio-installer are recently
added packages to the archive that did not exist in previous
versions.

Not purging them makes the process inconsistent and problematic,
as at least ubuntustudio-live cannot be installed due to the lack
of dependencies.

Refer only to source packages of Ubuntu fonts

See merge request trisquel/ubuntu-purge!38

* purge-bionic (REMOVE): Refer only to source packages.
	Upstream renamed ubuntu-font-family-sources to fonts-ubuntu.
* purge-* (REMOVE): Refer only to source packages.

Signed-off-by: Adonay Felipe Nogueira <adfeno@hyperbola.info>

Remove Ubuntu fonts

See merge request trisquel/ubuntu-purge!37

This is an attempt to fix https://trisquel.info/en/issues/27032

 .

* purge-* (REMOVE): Remove Ubuntu fonts.

Signed-off-by: Adonay Felipe Nogueira <adfeno@hyperbola.info>

Drop python-pip's derivatives because the repos don't have the GFSD guarantee

See merge request trisquel/ubuntu-purge!33

Fix Bug 24895 - kubuntu-desktop still in repo

See merge request trisquel/ubuntu-purge!36

kubuntu-meta should be blocked to prevent branding isssues and issues
with meta packages who depend on non-free software.

Fixes part of https://trisquel.info/en/issues/20439 and all of
https://trisquel.info/es/issues/3741 .