This commit replaces a `waitForTimeout` occurrence with an equivalent
`waitForSelector` expression, and removes two other `waitForTimeout`
occurrences that are obsolete because we already wait for an observable
event to trigger or class change to happen.
Note that the other `waitForTimeout` occurrences in this file are either
part of #17931 or remain until we find a good way to ensure that nothing
happened (because currently there is nothing we can await there).