um: Don't garbage collect in deactivate_all_fds()

My previous commit didn't actually address the whole issue with
lockdep shutdown, I had another local modification that disabled
lockdep but that wasn't sufficient alone, so had to do the other
change.

Another issue remained though - during kfree() we acquire locks
and lockdep tries to annotate those with exactly the same issue
in the other patch - we no longer have "current".

So, just remove the garbage collection. There's no value in it
anyway since we're going to shut down anyway and marking a slab
object as free is now not very useful anymore.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Richard Weinberger <richard@nod.at>