INCR-265 Run python-modernize on lms/djangoapps/courseware/management and lms/djangoapps/courseware/tests (#20716)

* updated files according to INCR-265

* fixed docstring and line-length problems from quality test

* Revert "fixed docstring and line-length problems from quality test"

This reverts commit d050f55a4ecfaa38f46b80ec4bb85ff399a79a8c.

* fixed errors reported in quality report

* had error, fixed it

* reversed change

* fixed over/under indentation, and added line to import.py that Ned had suggested

* tried disabling pylint for this line

* testing new email

* testing email in different window

* re-added symlink and docstring