Remove incorrect default from docs

[Dreamsorcerer]

Fixes #5827

[Dreamsorcerer]

Not sure the optional/default actually needs to be said, given that it can be seen in the function signature. But, that's a separate task if someone wants to clean that up.

[codecov]

Codecov Report

Merging #5828 (f9714e5) into master (38c396b) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #5828   +/-   ##
=======================================
  Coverage   96.75%   96.75%           
=======================================
  Files          44       44           
  Lines        9849     9849           
  Branches     1591     1591           
=======================================
  Hits         9529     9529           
  Misses        182      182           
  Partials      138      138           

Flag	Coverage Δ
unit	96.64% <ø> (ø)

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[AustinScola]

Any reason not to merge this?

[patchback]

Backport to 3.8: 💚 backport PR created

✅ Backport PR branch: patchback/backports/3.8/60f57272ab1ac230b2e5a3c8eca9f3ccf9c24252/pr-5828

Backported as #5899

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