remove docutils.nimble (not a real nimble package, and affected canonical imports)

[timotheecour]

follows #16999
refs #16999 (comment)

after PR, docs for highlight show as packages/docutils/highlite which is now correct, instead of highlite; indeed, packages/docutils/highlite works, import highlight doesn't work

future work

• I've removed the only use of Tip::, docs for rst should mention this admonication somewhere

## .. Tip:: Import ``packages/docutils/rst`` to use this module
##    programmatically.

• figure out what to do with nimsuggest/sexp.nim; it has an incorrect nimble package structure since we have:

nimsuggest/nimsuggest.nimble
nimsuggest/sexp.nim

as a result, its docs have this note:

## **Note:** Import ``nimsuggest/sexp`` to use this module

because the computed canonical import is sexp instead of nimsuggest/sexp

• add nimforum to important_packages

[dom96]

I think this is a breaking change. It will break the forum at least.

Maybe we just need to move it to the stdlib? Including Nimble packages as part of Nim is tricky unfortunately. We should do our best to keep backwards compat in any case.

[timotheecour]

I think this is a breaking change. It will break the forum at least.

why is it a breaking change and how do i reproduce the breakage you're referring to?
nimforum has things like:

# src/utils.nim:
import rstgen

# src/nim.cfg:
path="$lib/packages/docutils"

but I don't why this PR would cause a breakage

on a related note, can you add nimforum to important_packages?

[Araq]

We'll add nimforum to important_packages later and see how it can compile with this patch applied.