osd/osd_types: remove useless encode_compat local var for pg_pool_t::encode

This is left over from db3fd1152a87f8f152facdf141f8367296b371df
when we made the HitSet stuff incompat, but that behavior was reverted by
dc3ce58add130ca5a0a20b097b0ac934a1b486c7, leaving this cruft behind.

Signed-off-by: Sage Weil <sage@redhat.com>
osd/osd_types: be pedantic about encoding last_force_op_resend without feature bit

The addition of the value is completely backward compatible, but if the
mon feature bits don't match it can cause monitor scrub noice (due to the
parallel OSDMap encoding).  Avoid that by only adding the new field if the
feature (which was added 2 patches after the encoding, see
3152faf79f498a723ae0fe44301ccb21b15a96ab and
45e79a17a932192995f8328ae9f6e8a2a6348d10.

Fixes: #8815
Backport: firefly
Signed-off-by: Sage Weil <sage@redhat.com>
Merge pull request #2094 from ceph/wip-8815

mon: avoid scrub noise due to divering OSDMap encoding versions

Reviewed-by: Greg Farnum <greg@inktank.com>