Switch SignatureTest to repackaged junit/android.test

Removes the dependency on junit and android.test classes to allow the
test to work when they are not present.

Tested using:
    m -j32 CtsApiSignatureTestCases && \
        cts-tradefed run cts -a arm64-v8a -m CtsApiSignatureTestCases

Follow on from If0355a0d50b7540f416d464fdf7ffae0e4766b1c

Bug: 35192974
Bug: 30188076
Test: see above
Change-Id: I414d0500730541b692a20073820fa0566130d16f
4 files changed