Add TBB artifacts to .gitignore

Add the following to fenix/app/.gitignore

/android-release.aar
/jsocksAndroid-release.aar
/service-release.aar
/universal-0.0.3.jar
/src/main/assets/extensions/{73a6fe31-595d-460b-a920-fcc0f8843232}.xpi

Android