Fix #23885: Skip capture sets in checkNoPrivateLeaks and drop them in posttyper when cc is not enabled

[noti0na1]

Fix #23885

[sjrd]

I thought all cc-related annotations were immediately dropped and never visible to non-cc users. If they end up here, doesn't that means that early drops were missed?

If they are not dropped early, how do you prevent the annotations (or their pretty-printed form) never to appear in error messages, for example?

[noti0na1]

I guess CleanupRetains was designed to drop any capture annotation in non-cc code, but ends up drop nothing. If we want prevent capture annotation showing in any error message, we should drop them in typer.