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
```
6065a0daab