Remove 8 unnecessary stubbings in PiwikTrackerTest.java

[ARUS2023]

In our analysis of the project, we observed that there are 6 tests: PiwikTrackerTest.testSendBulkRequestAsync_Iterable, PiwikTrackerTest.testSendBulkRequestAsync_Iterable_StringFF, PiwikTrackerTest.testSendBulkRequestAsync_Iterable_StringFT, PiwikTrackerTest.testSendBulkRequestAsync_Iterable_StringTT, PiwikTrackerTest.testSendBulkRequest_Iterable_StringTT, PiwikTrackerTest.testSendRequestAsync contain 8 unnecessary stubbings in total.

Unnecessary stubbings are stubbed method calls that were never realized during test execution. Mockito recommends to remove unnecessary stubbings (https://www.javadoc.io/doc/org.mockito/mockito-core/latest/org/mockito/exceptions/misusing/UnnecessaryStubbingException.html).

We propose below a solution to remove the unnecessary stubbings.

[dheid]

Thanks, @ARUS2023 !