Summary:
This reverts a3931e9531
The open source `test_android` job is not configured to use Android 26 quite yet. I've spent a couple of days trying to get our Android tests back in working order, with no luck.
I'm reverting the change that bumped React Native to use build tools 26 + Android SDK 26. I encourage contributors interested in making this change happen to work on getting our Android tests working with API 26.
This will allow us to focus on getting `test_android` back to green, and _then_ we can work on bumping to API 26 while keeping tests green.
Reviewed By: fkgozali
Differential Revision: D8066226
fbshipit-source-id: 9bfd58a7f081c0971b78b331073e70545c21ca6d