Fix the DeprecationWarning for unescape (#23936)

This PR solves the DeprecationWarning mentioned in:
https://build.testeng.edx.org/job/edx-platform-python-pipeline-master/warning_5freport_5fall_2ehtml/

HTMLParser was renamed in html.parser in Python3:
https://docs.python.org/2/library/htmlparser.html#module-HTMLParser

* html_parser.HTMLParser().unescape from six.moves has been deprecated

* instead use html.unescape from Python3

Documentation for unescape in Python3:
https://docs.python.org/3/library/html.html#html.unescape

- html_parser from six.moves has been deprecated

- instead use html.parser from Python3

- Order imports using isort

- Delete unused import crum