Disable unused Python 2 variant. am: f3568df232 am: 08959a10d4

Original change: https://android-review.googlesource.com/c/platform/external/python/google-auth-library-python/+/2221605

Change-Id: I8bb4db3c3de3eb62e9b5cc9e2411f2bdfae1a0f0
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>