check-flagged-apis: simplify unit test dependencies

Replace the current unit test runner DeviceJUnit4ClassRunner with JUnit4
and replace the (larger) dependency tradefed with the (smaller)
dependency junit.

This has no impact other than minimizing the unit test static_libs.

Bug: 334870672
Test: atest --host check-flagged-apis-test
Change-Id: I0520ab0feeea5ea2ed15905136ba2647f86162cb