Crashes UI: Don't require ConsentLevel::kSync for is_internal check

CrashesDOMHandler contains logic to check whether the signed-in account
is an @google.com account.
Before this CL, that check required ConsentLevel::kSync, i.e. for the
user to have enabled Sync-the-feature.
This is just an historic artifact; there's no need for this check to
depend on Sync-the-feature.
So this CL changes this to ConsentLevel::kSignin.

Bug: 40066882
Change-Id: Ib74cf5cb0eeebb3c590c99003236a9aadd822479
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5377795
Auto-Submit: Marc Treib <treib@chromium.org>
Reviewed-by: Mikel Astiz <mastiz@chromium.org>
Commit-Queue: Mikel Astiz <mastiz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1274233}