ocfs2: Remove ->unblock lockres operation

Have ocfs2_process_blocked_lock() call ocfs2_generic_unblock_lock(), which
gets to be ocfs2_unblock_lock() now that it's the only possible unblock
function.

Remove the ->unblock() callback from the structure, and all lock type
specific unblock functions.

Signed-off-by: Mark Fasheh <mark.fasheh@oracle.com>