Revert "Discard STUN attributes that follow MESSAGE-INTEGRITY"

This reverts commit 5ec4c28c1f05241445020a85b3ff295c4ed0b270.

Reason for revert: Blocks import to first party projects: STUN tests fail.

Original change's description:
> Discard STUN attributes that follow MESSAGE-INTEGRITY
>
> Bug: chromium:504567957
> Change-Id: I59a722da83c9a44c9c9cf6285a089b719f10dc82
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/465503
> Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
> Auto-Submit: Harald Alvestrand <hta@webrtc.org>
> Commit-Queue: Harald Alvestrand <hta@webrtc.org>
> Cr-Commit-Position: refs/heads/main@{#47505}

Bug: chromium:504567957
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Change-Id: I2e3b8cf7a6d083caee712bbc5aef4188b52733c8
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/465882
Bot-Commit: rubber-stamper@appspot.gserviceaccount.com <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Ilya Nikolaevskiy <ilnik@webrtc.org>
Owners-Override: Ilya Nikolaevskiy <ilnik@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#47512}