Remove PasswordProtection population metrics

This CL removes metrics tracking the population of users at the
start of the request vs at the time of ping as they failed to find
any meaningful race condition in the Safe Browsing preference checks.

Fixed: 1261113,1261112
Change-Id: Ib490a24b3bbd86b469f1411f6ef8646d289f4e20
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3414054
Commit-Queue: Daniel Rubery <drubery@chromium.org>
Auto-Submit: Daniel Rubery <drubery@chromium.org>
Reviewed-by: Xinghui Lu <xinghuilu@chromium.org>
Commit-Queue: Xinghui Lu <xinghuilu@chromium.org>
Cr-Commit-Position: refs/heads/main@{#962798}