Rename desktop file

For 3.10, lots of applications are renaming their desktop files as it's
required to use D-Bus activation. There's no longer any point in
maintaining our old desktop file name just to ensure the app doesn't
disappear from user favorites, as other apps will be disappearing
regardless of what we do.
Do not remove unregeneratable files in distclean

distclean should not remove anything that can't be regenerated by
running configure. All of this stuff should be removed by
maintainer-clean instead.
Use git.mk