cifs: get rid of dns resolve worker

We already upcall to resolve hostnames during reconnect by calling
reconn_set_ipaddr_from_hostname(), so there is no point in having a
worker to periodically call it.

Signed-off-by: Paulo Alcantara (SUSE) <pc@manguebit.com>
Reviewed-by <lsahlber@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>