Clear inline mocks in MockSystemRule

Fix memory leaks in tests that use MockSystemRule. See
https://github.com/mockito/mockito/issues/1614 for more information on
what is causing the memory leaks.

This will not address all the memory leaks in
FrameworksMockingServicesTests since there are many other tests that
does not use MockSystemRule but does use ExtendedMockito that still
needs to be fixed.

Bug: 300996262
Test: atest
Change-Id: I6d78b677b52b1b9a07c95f73d9d393604b29f393