[WIP] Merge upstream

**:warning: NOT READY TO MERGE :warning:**

This pull request:

 * Updates to the [3.0.2](https://github.com/AliSoftware/OHHTTPStubs/releases/tag/3.0.2) tag
 * Removes our custom code changes, since upstream has significantly improved since we made them (hopefully rendering them unnecessary)
 * Removes OHHTTPStubsDemo from the WD
 * Removes AFNetworking as a submodule