osd/MissingLoc, PeeringState: remove osd from missing loc in purge_strays()

osd/MissingLoc, PeeringState: remove osd from missing loc in purge_strays()

We should always try to keep osds in missing_loc consistent with peer_missing
and peer_info. When we remove an osd from peer_missing and peer_info, we
should also remove it from missing_loc during purging strays.

Signed-off-by: Neha Ojha <nojha@redhat.com>
(cherry picked from commit 624ade487ea4aeaf988cc1767e0b293f76addd5b)

Conflicts:
	src/osd/MissingLoc.cc
	src/osd/MissingLoc.h
	src/osd/PeeringState.cc
- these files do not exist in luminous; made the changes manually to
  src/osd/PG.cc and src/osd/PG.h
- ldout(cct, ...) -> ldout(pg->cct, ...)