dlm: drop kobject release callback handling

This patch removes the releasing of the "struct dlm ls" resource out of
the kobject handling. Instead we run kfree() after kobject_put() of the
lockspace kobject structure that should always being the last put call.
This prepares to split the releasing of all lockspace resources
asynchronously in the background and just deregister everything in
release_lockspace().

Signed-off-by: Alexander Aring <aahringo@redhat.com>
Signed-off-by: David Teigland <teigland@redhat.com>