Remove stetho (#762)

Summary:
## Summary

Resolves https://github.com/facebook/flipper/issues/607

This removes stetho dependencies directly in favor of just copying in the used classes. This removes the last non-androidx dependency from the project, and is useful as stetho appears to be unmaintained. The fresco stetho dependency appeared to be completely unused.

## Changelog

Remove stetho dependencies. It was unused other than a few utility methods, but came at the cost of preventing Flipper consumers from completely removing dependencies that hadn't updated to Androidx yet.
Pull Request resolved: https://github.com/facebook/flipper/pull/762

Test Plan: Existing tests still pass with no regressions. Functionally this should be no difference.

Reviewed By: jknoxville

Differential Revision: D19577969

Pulled By: passy

fbshipit-source-id: b277ddf97a9d2c846dd0b9227c02bb46c1ecd930

build.gradle

@@ -86,7 +86,6 @@ ext.deps = [
         junit              : 'junit:junit:4.12',
         hamcrest           : 'org.hamcrest:hamcrest-library:1.3',
         mockito            : 'org.mockito:mockito-core:1.9.5',
-        stetho             : 'com.facebook.stetho:stetho:1.5.1',
         okhttp3            : 'com.squareup.okhttp3:okhttp:3.14.1',
         leakcanary         : 'com.squareup.leakcanary:leakcanary-android:1.6.3',
         testCore           : 'androidx.test:core:1.1.0',