Merge pull request #17607 from liewegas/wip-post-luminous-more-mon

mon: post-luminous cleanup (part 3 of ?)

Reviewed-by: Greg Farnum <gfarnum@redhat.com>

diff --cc src/mon/MgrStatMonitor.cc
Simple merge

diff --cc src/mon/Monitor.cc
Simple merge

diff --cc src/mon/OSDMonitor.cc
Simple merge

diff --cc src/mon/PGMap.cc
Simple merge