Unit tests: cleanup of outdated / unused / commented out code

Many methods in unit tests were unused, in particular in mocks, where methods overriding in the past were not overriding anything anymore.

Some commented out code was referring to features that seem to have been removed years ago, so I removed it as well.

`HydratorMockStatement::bindParam()` was adding extra parameters that its parent did not define, and that were never used, so I removed them as well.