Disable unused Python 2 variant. am: f3568df232 am: 08959a10d4 am: 5908c1292b

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

Change-Id: If63c5f35a293daac9ac7a86d74cf57ac10b7a9bf
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>