Add visibility for TetheringCoverageTests

1. NetworkStackTestsLib can be visible to TetheringCoverageTests
2. NetworkStackJarJarRules can be visible to
   TetheringIntegrationTestsDefaults
3. Remove uncessary lib "libartbase" because
   it's not visible to TetheringCoverageTests.

Bug: 148636687
Test: atest NetworkStackTests
      atest TetheringCoverageTests
Change-Id: I0e0d597a968f99f4a99c3d7ab014af4e144ab40f