Remove max headers parameter

[starflows]

What do these changes do?

The unused parameter max_headers is removed from HeadersParser.

Are there changes in behavior for the user?

No.

Related issue number

#6721

Checklist

• I think the code is well written
• Unit tests for the changes exist
• Documentation reflects the changes
• If you provide code modification, please add yourself to CONTRIBUTORS.txt
  • The format is <Name> <Surname>.
  • Please keep alphabetical order, the file is sorted by names.
• Add a new news fragment into the CHANGES folder
  • name it <issue_id>.<type> for example (588.bugfix)
  • if you don't have an issue_id change it to the pr id after creating the pr
  • ensure type is one of the following:
    • .feature: Signifying a new feature.
    • .bugfix: Signifying a bug fix.
    • .doc: Signifying a documentation improvement.
    • .removal: Signifying a deprecation or removal of public API.
    • .misc: A ticket has been closed, but it is not of interest to users.
  • Make sure to use full sentences with correct case and punctuation, for example: "Fix issue with non-ascii contents in doctest text files."

[Dreamsorcerer]

I think it's probably best not to backport to 3.9, as it's not backwards compatible and might break someone's code.

[codecov]

Codecov Report

Merging #6725 (d8f1a4c) into master (adeece3) will decrease coverage by 71.68%.
The diff coverage is 0.00%.

@@             Coverage Diff             @@
##           master    #6725       +/-   ##
===========================================
- Coverage   93.44%   21.76%   -71.69%     
===========================================
  Files         104      104               
  Lines       30629    30627        -2     
  Branches     3076     3076               
===========================================
- Hits        28622     6666    -21956     
- Misses       1838    23849    +22011     
+ Partials      169      112       -57     

Flag	Coverage Δ
unit	21.74% <0.00%> (-71.63%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
aiohttp/http_parser.py	18.54% <0.00%> (-74.20%)	⬇️
aiohttp/web_protocol.py	18.05% <ø> (-71.64%)	⬇️
tests/test_http_parser.py	18.68% <ø> (-80.40%)	⬇️
tests/test_client_ws_functional.py	6.41% <0.00%> (-91.83%)	⬇️
tests/test_client_functional.py	8.64% <0.00%> (-89.86%)	⬇️
tests/test_client_ws.py	10.81% <0.00%> (-89.19%)	⬇️
tests/test_web_app.py	10.47% <0.00%> (-89.01%)	⬇️
tests/test_web_functional.py	9.15% <0.00%> (-88.89%)	⬇️
tests/test_web_sendfile.py	11.76% <0.00%> (-88.24%)	⬇️
tests/test_streams.py	11.99% <0.00%> (-88.01%)	⬇️
... and 87 more

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