scsi: sd: remove check_events callback

->check_events() callback sends the Test Unit Ready command to check if
underlying media state has changed or not, this is generally not required
for embedded storage media (such as UFS). We have seen race between Test
Unit Ready command and runtime suspend context which basically can put
the Test Unit Ready command at the head of the request queue when queue's
rpm_status is SUSPENDING. In this case, scsi_request_fn will not pull in
the Test Unit Ready command as REQ_PM flag is not set for it. This
basically causes the deadlock situation. Currently there is no better way
to fix this error other than removing the check_events() callback which is
anyway not required for embedded storage like UFS.

Change-Id: Idac374ba1674fede38cb3dcfc2c1f8d3db234d1d
Signed-off-by: Subhash Jadavani <subhashj@codeaurora.org>