mm: Remove support for kmem_cache_name()

The last user was ext4 and Eric Sandeen removed the call in a recent patch. See
the following URL for the discussion:

http://marc.info/?l=linux-ext4&m=129546975702198&w=2



Signed-off-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>