osd: Replace active/pending scrub tracking for local/remote

osd: Replace active/pending scrub tracking for local/remote

This is similar to how recovery reservations are split between
local and remote.

It was the case that scrubs_pending was used for reservations at
the replicas as well as at the primary while requesting reservations
from the replicas.  There was no need for scrubs_pending to turn
into scrubs_active at the primary as nothing treated that value
as special.  scrubber.active = true when scrubbing is
actually going.

Now scurbber.local_reserved indicates scrubs_local incremented
Now scrubber.remote_reserved indicates scrubs_remote incremented

Fixes: https://tracker.ceph.com/issues/41669
Signed-off-by: David Zafman <dzafman@redhat.com>