Cleanup VpnTest for unused methods/annotations

• Remove unused private methods
• Build files have this test in FrameworksNetTests, which
  by TEST_MAPPING is not run on T and below. It is not in
  the targets that do run on T and below like
  ConnectivityCoverageTest.

Test: VpnTest
Change-Id: I198e5b3571e34e41611f71d351501d3f98f78caa
1 file changed