Python aarch64 linux tests broken by recent piper import

[jtattermusch]

After this diff: 998d3a3...636132b from
#8617

the linux/python_aarch64 test got broken (and has been failing since)
https://source.cloud.google.com/results/invocations/53e39cd8-0d19-4f6e-a06c-d81f72a0c8e2/log

[jtattermusch]

The diff from piper import seems to be reverting some of the python's setup.py changes introduced by #8280 (and those changes are necessary for generating the aarch64 wheels).

added by the aarch64 PR:
https://github.com/protocolbuffers/protobuf/pull/8280/files#diff-eb8b42d9346d0a5d371facf21a8bfa2d16fb49e213ae7c21f03863accebe0fcf

and seems to be removed by the piper import diff:
998d3a3...636132b#diff-eb8b42d9346d0a5d371facf21a8bfa2d16fb49e213ae7c21f03863accebe0fcf