plugin: clean up redundant in-docstring parameter type annotations

[dgw]

Description

I realized that leaving parameter types in the docstrings of these decorators is a maintenance nightmare waiting to happen. Our docs show the type-hints in the function signatures very nicely now. Putting types in the parameter list too is just redundant.

Checklist

• [x] I have read CONTRIBUTING.md
• [x] I can and do license this contribution under the EFLv2
• [x] No issues are reported by make qa (runs make lint and make test)
  • I mean there'd better not be any, since I didn't touch code.
• [x] I have tested the functionality of the things this change touches
  • By this I mean I test-built the docs locally. Sphinx still warns about some type annotations/x-refs that it has trouble resolving, but those aren't new (discussed in #2496 and variously on IRC).

[dgw]

I'm going to rebase with a few more tweaks ahead of @SnoopJ's rereview. Found some more things I could clean up, in particular some of the more confusing decorator type-hints (plugin no longer even imports typing.Any in my local copy 🥳).

[dgw]

13:20:57 <+dgw> SnoopJ, did you want to take another look at #2539 or should I just ship it?
13:21:38 <+SnoopJ> nah, ship it