clean up UX revamp flag in SearchActivityLocationBarLayout

This CL updates the padding for the SearchActivityLocationBarLayout,
which use the location_bar_start_padding_modern as default.
We did not update the background default tint and corner radius,
because in Chrome, the tint is changing between normal and incognito
mode, and the radius is changing between focus and non-focus.

Change-Id: I78498a2b0bd28a3a0e62d5eff4e85f46c0550ff3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5426410


Commit-Queue: Gang Wu <gangwu@chromium.org>
Reviewed-by: Sky Malice <skym@chromium.org>
Reviewed-by: Tomasz Wiszkowski <ender@google.com>
Cr-Commit-Position: refs/heads/main@{#1283163}