Removed duplicate timeout parameter in ClientSession reference docs.

[gdub]

What do these changes do?

Removed duplicate timeout parameter in ClientSession reference docs.

Are there changes in behavior for the user?

n/a

Related issue number

n/a

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."

[codecov]

Codecov Report

Merging #5262 (2ea2e9f) into master (6f73339) will decrease coverage by 0.46%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #5262      +/-   ##
==========================================
- Coverage   97.54%   97.07%   -0.47%     
==========================================
  Files          43       43              
  Lines        8794     8794              
  Branches     1415     1415              
==========================================
- Hits         8578     8537      -41     
- Misses        101      135      +34     
- Partials      115      122       +7     

Flag	Coverage Δ
unit	96.95% <ø> (-0.43%)	⬇️

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

Impacted Files	Coverage Δ
aiohttp/web_runner.py	92.44% <0.00%> (-5.34%)	⬇️
aiohttp/tcp_helpers.py	94.73% <0.00%> (-5.27%)	⬇️
aiohttp/pytest_plugin.py	92.50% <0.00%> (-5.00%)	⬇️
aiohttp/connector.py	94.88% <0.00%> (-1.92%)	⬇️
aiohttp/web.py	97.45% <0.00%> (-1.70%)	⬇️
aiohttp/web_protocol.py	91.14% <0.00%> (-1.15%)	⬇️
aiohttp/test_utils.py	99.06% <0.00%> (-0.63%)	⬇️

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[aio-libs-github-bot]

💚 Backport successful

The PR was backported to the following branches:

• ✅ 3.7
• ✅ 3.8