Remove ~func type params in parallel package

[bobg]

Forgot this before creating the v4.0.0 release (which is now retracted in favor of v4.1.0): removing the ~func(...) type parameters from the functions in parallel.

[github-actions]

Modver result

This report was generated by Modver,
a Go package and command that helps you obey semantic versioning rules in your Go module.

This PR requires an increase in your module’s major version number.
If the new major version number is 2 or greater,
you must also add or update the version suffix
on the module path defined in your go.mod file.
See the Go Modules Reference for more info.

checking Pool
  in type parameters of func[T, U any, F ~func(T) (U, error)](n int, f F) func(T) (U, error)
    went from 3 type parameter(s) to 2
      Major

[coveralls]

Pull Request Test Coverage Report for Build 10429263492

Details

• 4 of 4 (100.0%) changed or added relevant lines in 1 file are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.4%) to 91.068%

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Files with Coverage Reduction	New Missed Lines	%
parallel/parallel.go	2	79.17%

Totals
Change from base Build 10421785002:	-0.4%
Covered Lines:	469
Relevant Lines:	515

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💛 - Coveralls