Fix "gradle -PunityExe=/path/to/unity/editor" (#82)
Fix "gradle -PunityExe=/path/to/unity/editor" (#82)

Removed some code that was adapted from other Google Unity gradle files, e.g.
https://github.com/googlesamples/google-signin-unity/blob/master/build.gradle#L47

Specifying the Unity Editor executable path from the command line seems
to work better without that code.
google/play-instant-unity-plugin