mgr/Mgr.cc: clear daemon health metrics instead of removing down/out osd from daemon...

mgr/Mgr.cc: clear daemon health metrics instead of removing down/out osd from daemon state

Reverts the change from https://github.com/ceph/ceph/pull/53993
and directly clears daemon health metrics for down and out OSDs.
The former approach of removing down/out OSDs from the daemon
state has undesirable consequences for stat output, including
the prometheus exporter.

Fixes: https://tracker.ceph.com/issues/66168
Signed-off-by: Cory Snyder <csnyder@1111systems.com>