Improve description of URL-keyed data collection policy.

The previous wording had grammar errors.

The new wording matches what we use for some other policies.

Bug: None
Change-Id: I938585cbcfd49c3dc2d68eb156301ee16a52ad89
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3876744


Reviewed-by: Julian Pastarmov <pastarmovj@chromium.org>
Commit-Queue: Alexei Svitkine <asvitkine@chromium.org>
Reviewed-by: Robert Kaplow <rkaplow@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1045875}