cifs: remove unused stats

These timers were a good idea but weren't used in current code,
and the idea was cifs specific.  Future patch will add similar timers
for SMB2/SMB3, but no sense using memory for cifs timers that
aren't used in current code.

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