[Autofill Assistant] Remove WaitForDocumentToBecomeInteractive

Replaced by WaitUntilDocumentReadyState (which is WaitForDocumentReady
State with ignoring the result data).

This also changes the settings from being round based to using a
single timeout.

Bug: b/172542134
Change-Id: I339f698cc37f9c028bb25a8a04c4248404b21b84
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2529101
Commit-Queue: Sandro Maggi <sandromaggi@google.com>
Reviewed-by: Mathias Carlen <mcarlen@chromium.org>
Reviewed-by: Stephane Zermatten <szermatt@chromium.org>
Cr-Commit-Position: refs/heads/master@{#826813}