[Autofill] Simplify ExtractFormDataWithFieldsAndFrames()

This CL eliminates the `extracted_elements` variable and uses
`control_elements` instead and removes a now-redundant `continue`.
It also simplifies the call of MatchLabelsAndFields().

Bug: 40100455
Change-Id: I907e65ac36a933c321bd80ba83dd6064a641c523
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5800630
Code-Coverage: findit-for-me@appspot.gserviceaccount.com <findit-for-me@appspot.gserviceaccount.com>
Reviewed-by: Jihad Hanna <jihadghanna@google.com>
Commit-Queue: Christoph Schwering <schwering@google.com>
Cr-Commit-Position: refs/heads/main@{#1344946}