cifs: remove [gu]id/backup[gu]id/file_mode/dir_mode from cifs_sb

We can already access these from cifs_sb->ctx so we no longer need
a local copy in cifs_sb.

Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>