target: Delete tmr from list before processing

This patch does an explicit list_del_init(tmr->tmr_list) in
core_tmr_drain_tmr_list() before starting processing of
outstanding TMRs to abort, instead of explicitly checking
which TMR descriptor matches the caller.

Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Disseldorp <ddiss@suse.de>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>