Remove the "Widths" section from the OuiModal docs

[joshuarrrr]

In https://oui.opensearch.org/1.0/#/layout/modal, we have a section about how to manually specify widths via inline styles. This seems like a bit of an antipattern, and not something we want to encourage. See #783 for examples where we do customize modal widths today.

If we do want to allow direct sizing controls, we probably want to add more props. Otherwise, I think we should just scratch the section altogether.

[KrooshalUX]

I agree that we should remove this guidance - it does not align with the Design System directive to rely on the responsive system as much as possible out of the box.

[BigSamu]

@joshuarrrr @BSFishy can I take this issue?

[BSFishy]

Yep, looks like this is ready to pick up

[BSFishy]

Fixed in #1066