Merge pull request #38374 from rzarzynski/wip-crimson-backfill-remove

crimson: add support for backfill, part 2 -- MOSDPGBackfillRemove

Reviewed-by: Kefu Chai <kchai@redhat.com>

diff --cc src/crimson/osd/backfill_state.cc
Simple merge

diff --cc src/crimson/osd/backfill_state.h
Simple merge

diff --cc src/crimson/osd/osd.cc
Simple merge

diff --cc src/crimson/osd/pg.h
Simple merge

diff --cc src/crimson/osd/pg_recovery.cc
Simple merge

diff --cc src/test/crimson/test_backfill.cc
Simple merge