* Migrate the bm_diff benchmarks to python3

Includes a requirements.txt pinned at ~2017 versions, when this script
was first written.

* Replace p2 with p3 scipy/numpy dependencies.

* py2->3 for benchmark setup scripts

* upgrade pip to resolve python3 cryptography/setuptools-rust problem

* re-add jobset import (accidentally removed)

* re-add six's urllib import. This file is still used in py2 tests

* force py3 in run_if_c_cpp_modified.sh

* Fix another instance of subprocess.check_output binary mode

* Use the requirements.txt for CI perf environment setup

* Try to upgrade PyJWT. (v2.0.0 was problematic, #25053)

v2.x makes encode return strs from jwt.encode in both py2 and py3.
Previously, py3 would return bytes, and py2 a str.

* upgate cryptography lib version requirements for jwt.

* Wrap pip requirements specifier in quotes '>=x,<y'

* Decode subprocess output once instead of for every line

* Revert "Decode subprocess output once instead of for every line"

This reverts commit 28d14026431622ac7afd3535a8d7118e5be96628.

py2 doesn't support the `text` argument to subprocess.check_output.

* Address reviewer requests

* Pin a valid scipy version

* Remove scipy and tabulate dependencies from macos tests