Automatic merge from submit-queue

Minor cleanup to scheduler.

Part 1 of pr for scheduler modularization specifically supporting CheckServiceAffinity improvements #33763.

These are some innoccous changes which help separate the predicate injection machinery from the cleanup parts of CheckServiceAffinity

@timothysc @wojtek-t

- changes to metadata.go are for the follow on pr
- changes to prio/pred stuff is all passing unit tests

hoping to grease this through and then the interesting part is in the follow on pr.