The observer was moved and is now bound to the activity and its
context. If the activity is re-created we leak the observer and
therefore the activity itself.
With this we make sure to stop the observer and also don't use
the activity context to begin with.
This is how we can apply the new test runner to remove duplication.
This commit was generated programmatically with the following commands:
```
// Replace test runners with new one.
find app/src/test -type f -exec gsed -i "s/@RunWith(RobolectricTestRunner::class)/@RunWith(FenixRobolectricTestRunner::class)/" {} +
find app/src/test -type f -exec gsed -i "s/@RunWith(AndroidJUnit4::class)/@RunWith(FenixRobolectricTestRunner::class)/" {} +
// Replace imports of old test runners with new one
find app/src/test -type f -exec gsed -i "s/org.robolectric.RobolectricTestRunner/org.mozilla.fenix.helpers.FenixRobolectricTestRunner/" {} +
find app/src/test -type f -exec gsed -i "s/androidx.test.ext.junit.runners.AndroidJUnit4/org.mozilla.fenix.helpers.FenixRobolectricTestRunner/" {} +
// Remove unused imports
find app/src/test -type f -exec gsed -i "/@Config(application = TestApplication::class)/d" {} +
find app/src/test -type f -exec gsed -i "/import org.mozilla.fenix.TestApplication/d" {} +
find app/src/test -type f -exec gsed -i "/import org.robolectric.annotation.Config/d" {} +
```
Where gsed is the GNU version of sed installed via homebrew. After
running these commands, I need to manually clean up the following files:
- FenixRobolectricTestRunner
- LocaleManagerExtensionTest
