Remove a handful of wait_for_requests calls

What does this MR do and why?

Remove a handful of wait_for_requests calls.

This resulted from a pilot run of a harness developed for Remove all uses of `wait_for_requests`, `wait_f... (#605815).

The initial runs are looking (a) "trivial" sites, where (b) they're the only wait_for_requests call in the whole file. "Trivial" sites: where wait_for_requests (which per #605815 can return at different times at different runs) is immediately followed by a waiting Capybara assertion that checks for what we care about. We can just let that do the waiting.

One of these cases was followed by a negative assertion (expect text not to appear); for robustness, I've added a corresponding (matching? heh) positive assertion immediately following the initial visit, so that we can be sure the content in question actually did disappear, and that we can't have meaningless passes where it wasn't present at all to begin with. See https://gitlab.com/kivikakk/wait-for-requests-cleanup-harness/-/blob/9cf53f5d/CATEGORY_NOTES.md for notes on this.

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