Removed gdx-pay-android-openiab.jar dependency

Currently one cannot run the android tests anymore, since there's a build path problem:

"The container 'Android Dependencies' references non existing library '...\libgdx\extensions\gdx-pay\gdx-pay-android-openiab\bin\gdx-pay-android-openiab.jar'.

The android tests project currently depends on the gdx-pay-android-openiab project anyway, so I think it's no problem to remove that "extra" dependency. I could still run the `PayTest`.