dlm: remove ls_local_handle from struct dlm_ls

This patch removes ls_local_handle from struct dlm_ls as it stores the
ls pointer of the top level structure itesef and this isn't necessary.
There is a lookup functionality to lookup the lockspace in
dlm_find_lockspace_local() but the given input parameter is the pointer
already. This might be more safe to lookup a lockspace but given a wrong
lockspace pointer is a bug in the code and we save the additional lookup
here. The dlm_ls structure can be still hidden by using dlm_lockspace_t
handle pointer.

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