docs: remove finished TODO

[nedbat]

TL;DR - [ A short summary of what this PR does and why ]

JIRA: JIRA-XXXX

What changed?

• [ More in depth breakdown of changes ]
• [ Peripheral things that got changed ]
• [ etc... ]

Developer Checklist

• Reviewed the release process
• Translations and JS/SASS compiled
• Bumped version number in openassessment/__init__.py and package.json

Testing Instructions

[ How should a reviewer test this PR? ]

Reviewer Checklist

Collectively, these should be completed by reviewers of this PR:

• I've done a visual code review
• I've tested the new functionality

FYI: @openedx/content-aurora

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@3d95b5d). Click here to learn what that means.
Patch has no changes to coverable lines.

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #2032   +/-   ##
=========================================
  Coverage          ?   95.09%           
=========================================
  Files             ?      158           
  Lines             ?    17446           
  Branches          ?     1625           
=========================================
  Hits              ?    16591           
  Misses            ?      641           
  Partials          ?      214           

Flag	Coverage Δ
unittests	95.09% <0.00%> (?)

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