[8229] Revert "[7746] Create a more user friendly external transform API"

[aaltay]

Reverts #9098

Py 3.7 tests are failing with a syntax error.

[aaltay]

R: @chadrik @robertwb @udim

[chadrik]

I introduced some tests of a feature that makes use of PEP526 syntax changes introduced in python 3.6. I got everything passing for the pre-commit tests but did not anticipate the post-commit problems. I'll get those fixed up ASAP.

[chadrik]

Note that the other solution to this is dropping support for python 3.5, but that's a bigger discussion.

[aaltay]

I was wrong in my JIRA issue. Py2 post commit is failing on py3.7 test. I thought py2 post commit was meant to skip these files.

[aaltay]

Run Portable_Python PreCommit

[aaltay]

Run Python 2 PostCommit

[aaltay]

Closing this. #9570 - addressed the test issues.