Revert "scanner: Add debug chrome://flags flag to override disclaimer"

This reverts commit 915a298658800bd4a470155a8ad37d85ac6b5b46.

Reason for revert: Removing expired debug flag

Original change's description:
> scanner: Add debug chrome://flags flag to override disclaimer
>
> See the previous CL (https://crrev.com/c/6356547) for implementation
> details. This is useful for developers and a11y testing.
>
> Bug: b:402981629
> Change-Id: I6a6a21005038194c9aef5258a8227e4c00b19537
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6356548
> Reviewed-by: Michelle Chen <michellegc@google.com>
> Commit-Queue: Michael Cui <mlcui@google.com>
> Cr-Commit-Position: refs/heads/main@{#1433899}

Bug: 427257915, b:402981629
Change-Id: I0c789a80e6e0327a8965879177d8108bd59e170a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6683098
Reviewed-by: Michelle Chen <michellegc@google.com>
Commit-Queue: Michael Cui <mlcui@google.com>
Cr-Commit-Position: refs/heads/main@{#1479636}