Clean up unused code in NewTabPageLayout

On tablets, only the scrollable MV tiles will show on NTP if feature
flag surface polish is enabled. Therefore, the code deleted in this CL
will never be called.

Bug: 331667743
Change-Id: Ic1fb62c1dcd10437f546f862aaead20a099fab3c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5402534


Reviewed-by: Xi Han <hanxi@chromium.org>
Commit-Queue: Xinyi Ji <xinyiji@chromium.org>
Reviewed-by: Sky Malice <skym@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1279864}