libceph: drop started parameter of __ceph_open_session()

libceph: drop started parameter of __ceph_open_session()

With the previous commit revamping the timeout handling, started isn't
used anymore.  It could be taken into account by adjusting the initial
value of the timeout, but there is little point as both callers capture
the timestamp shortly before calling __ceph_open_session() -- the only
thing of note that happens in the interim is taking client->mount_mutex
and that isn't expected to take multiple seconds.

Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Reviewed-by: Viacheslav Dubeyko <Slava.Dubeyko@ibm.com>