mgr/cephadm: drop osdspec_affinity tracking

mgr/cephadm: drop osdspec_affinity tracking

We identify which drivespec legacy OSDs belong(ed) to by metadata they
report to the mgr.  Modern cephadm does this instead by looking at the
'service' property in the unit.meta file.  Having cephadm query the osd
metadata is expensive for large clusters, so let's avoid this and rely
entirely on unit.meta.

Worst case, some upgraded clusters will show OSDs as service 'osd' instead
of service 'osd.whatever' for whatever drivespec created them.

Signed-off-by: Sage Weil <sage@newdream.net>