Remove milestones from documentation

[dafeda]

It has not been updated in a long time.

Pre review checklist

• Read through the code changes carefully after finishing work
• Make sure tests pass locally (after every commit!)
• Prepare changes in small commits for more convenient review (optional)
• PR title captures the intent of the changes, and is fitting for release notes.
• Updated documentation
• Ensured that unit tests are added for all new behavior (See
  Ground Rules),
  and changes to existing code have good test coverage.

Pre merge checklist

• Added appropriate release note label
• Commit history is consistent and clean, in line with the contribution guidelines.

[codecov-commenter]

Codecov Report

Merging #6203 (ef7ca7a) into main (68ff10b) will decrease coverage by 0.02%.
Report is 1 commits behind head on main.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #6203      +/-   ##
==========================================
- Coverage   82.66%   82.65%   -0.02%     
==========================================
  Files         347      347              
  Lines       21248    21248              
  Branches      833      833              
==========================================
- Hits        17565    17562       -3     
- Misses       3385     3388       +3     
  Partials      298      298              

see 2 files with indirect coverage changes

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