Bug 2357061

.Placement groups are not scaled down in `upmap-read` and `read` balancer modes Currently, `pg-upmap-primary` entries are not properly removed for placement groups (PGs) that are pending merge. For example, when the bulk flag is removed on a pool, or any case where the number of PGs in a pool decreases. As a result, the PG scale-down process gets stuck and the number of PGs in the affected pool do not decrease as expected. As a workaround, remove the `pg_upmap_primary` entries in the OSD map of the affected pool. To view the entries, run the `ceph osd dump` command and then run `ceph osd rm-pg-upmap-primary PG_ID` for reach PG in the affected pool. After using the workaround, the PG scale-down process resumes as expected.