Delete ibus.desktop

This is not an actual application, it just starts the daemon in the
background.  That's not something that should be in the application
list.  It should be started in the background when necessary.

BUG=http://code.google.com/p/ibus/issues/detail?id=1628

Review URL: https://codereview.appspot.com/9833043
Patch from Colin Walters <walters@verbum.org>.