Task: remove Invoker test/test_api incompatibility check

[srawlins]

I am writing a check into Mockito 4.0.0, and Mockito 3.0.3, that checks for an incompatibility between the test and test_api packages. It should be removed at some point.

[srawlins]

I believe the split for test_api and test_core happened around test 1.4.0, or maybe earlier. mockito now depends on test ^1.16.0, so I believe we can remove the check.