[css-grid] Remove deprecation message related to percentage rows

The behavior of percentage row tracks and gutters was updated
long time ago (M70), but we never remove the deprecation message
that was added before the change was shipped.
That message is not useful anymore so we should remove it.

The patch still keeps the use counter, as this behavior
hasn't been updated on Firefox yet. So it's nice to keep the statistics
of how many sites might be affected.

Updated the test expectations to remove the deprecation message.

BUG=846187

Change-Id: Ide2215b2c1527b87630a69dcc98cec27bc1963ca
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1796368
Reviewed-by: Javier Fernandez <jfernandez@igalia.com>
Reviewed-by: Philip J├Ągenstedt <foolip@chromium.org>
Commit-Queue: Manuel Rego <rego@igalia.com>
Cr-Commit-Position: refs/heads/master@{#695569}
12 files changed