os/bluestore: Fix dirty_range in BlueStore::_do_remove

os/bluestore: Fix dirty_range in BlueStore::_do_remove

dirty_range used to have length = 1 byte.
This is good if whole extent is inside shard.
But this has proven not to be the case.
dirty_range(offset, length) is slower only when it crosses shard.

Partially fixes: https://tracker.ceph.com/issues/70390

Signed-off-by: Adam Kupczyk <akupczyk@ibm.com>
(cherry picked from commit 4f566eaf6c4646e513ea6747c7df17383d8716e2)
(cherry picked from commit d6c61326a125f8bd278ec1c656d673e53edf47cd)
(cherry picked from commit 37248077f4550c85258b98f184193101a02dae0e)