`@callback` in JS files should not get export modifier, similar to `@typedef` fix

[jakebailey]

#1999 applied to @typedef, but other syntax like @callback and maybe even @overload also need to be careful to not confuse things; see #2044 (comment).

I am not sure if we have tests specifically for this case; the places I'm seeing a diff with @callback appear to be in files that are already modules through other means?

[ahejlsberg]

Hmm, I'm pretty sure the right fix here is to not include the export modifier in the reparsed JSTypeAliasDeclaration node that we generate for @callback. Similar to what I did for @typedef in #1999. The rest of the logic in #1999 will automatically handle @callback as well because at that point it's been turned into a JSTypeAliasDeclaration.

[jakebailey]

Yep, that's what I assumed too, I just forgot about these nodes when I was looking at your PR and only remembered them while looking at other bugs.