ceph: remove useless CEPHFS_FEATURES_CLIENT_REQUIRED

This macro was added but never be used. And check the ceph code
there has another CEPHFS_FEATURES_MDS_REQUIRED but always be empty.

We should clean up all this related code, which make no sense but
introducing confusion.
Signed-off-by: Xiubo Li <xiubli@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Luís Henriques <lhenriques@suse.de>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

fs/ceph/mds_client.h

@@ -42,7 +42,6 @@ enum ceph_feature_type {
 	CEPHFS_FEATURE_DELEG_INO,		\
 	CEPHFS_FEATURE_METRIC_COLLECT,		\
 }
-#define CEPHFS_FEATURES_CLIENT_REQUIRED {}
 
 /*
  * Some lock dependencies: