mon/Monitor.cc: notify_new_monmap() skips removal of non-exist rank

mon/Monitor.cc: notify_new_monmap() skips removal of non-exist rank

Problem:
In RHCS the user can choose to manually remove a monitor rank
before shutting the monitor down. Causing inconsistency in monmap.
for example we remove mon.a from the monmap, there is a short period
where mon.a is still operational and will try to remove itself from
monmap but we will run into an assertion in
ConnectionTracker::notify_ranks_removed().

Solution:
In Monitor::notify_new_monmap() we prevent the func
from going into removing our own rank, or
ranks that doesn't exists in monmap.

FYI: this is an RHCS problem only, in ODF,
we never remove a monitor from monmap
before shutting it down.

Fixes: https://tracker.ceph.com/issues/58049
Signed-off-by: Kamoltat <ksirivad@redhat.com>