Revisiting XAppKbdLayoutController

[JPeisach]

libgnomekbd is marked for removal in Debian, since it's been archived.

This has resulted in pretty much all the Cinnamon packages being marked for autoremoval in Debian.

I know that it was originally removed, and then got reverted in c22f968 - maybe it's time to revisit it?

The PRs in linuxmint/cinnamon#12758 all seem to have been merged.

[Fantu]

cinnamon still have something using it (even if for something "not critical"), rechecking it today if next version replaced also the latest part but still not, so I prepared this PR
Is there anything else in other components that still uses libgnomekbd and could cause errors and/or missing files? (that I didn't found) Regarding the xapp part, from a quick search seems that is no longer used.