Automatic merge from submit-queue (batch tested with PRs 46685, 49863, 50098, 50070, 50096)

Cover equivalence cache tests in scheduler core

**What this PR does / why we need it**:

Finish the last part of equivalence class scheduling #17390 : complete unit tests.

Also, removed `InvalidateCachedPredicateItemForPod` which is unused in latest design.

```
godep go test -v equivalence_cache_test.go  equivalence_cache.go  -cover

PASS
coverage: 92.3% of statements
ok  	command-line-arguments	0.071s
```

**Release note**:

```release-note
NONE
```