osd/MissingLoc.cc: do not rely on missing_loc_sources only

osd/MissingLoc.cc: do not rely on missing_loc_sources only

In 624ade487ea4aeaf988cc1767e0b293f76addd5b, we relied on missing_loc_sources
to check for strays and remove an OSD from missing_loc. However, it is
possible that missing_loc_sources is empty while there are still OSDs
present in missing_loc. Since the aim is to just remove a stray OSD from
missing_loc, we do not need to rely on missing_loc_sources. We still
clean missing_loc_sources if any stray is present in it.

Signed-off-by: Neha Ojha <nojha@redhat.com>