Use 'UTF-8' instead of 'utf8' as locale codeset suffix

This makes us work on OpenBSD's libc. GNU libc accepts both suffixes.

https://bugzilla.gnome.org/show_bug.cgi?id=710412
cc-common-language.c: Remove a bunch of unused code

This stopped being used in the last region panel re-design. See commit
35d920f1b887fb0f1df243e4d80ef8165a4f772e .

https://bugzilla.gnome.org/show_bug.cgi?id=710412
cc-common-language.c: Don't check if we have translations here

The list of locales returned from gnome_get_all_locales() already
filters out the locales for which we don't have translations so this
is a redundant check since users of get_initial_languages() only show
a language if it exists in gnome_get_all_locales() .

In fact, this code stopped working correctly since we started passing
locales including the codeset suffix to insert_language() because the
translation directories usually don't include the suffix and we
weren't stripping the suffix here.

https://bugzilla.gnome.org/show_bug.cgi?id=710412