[DOC] Remove optional from docstrings

[griegner]

Reference Issues/PRs

Fixes #1451

What does this implement/fix? Explain your changes.

Find optional \(default=(.*)\), replace with default=$1.

Does your contribution introduce a new dependency? If yes, which one?

None

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[TonyBagnall]

excellent, thanks, I probably would have ended up doing it manually :)

[MatthewMiddlehurst]

lgtm, had a quick scan and didnt see anything off.

[hadifawaz1999]

lgtm thanks