Remove expired contextual nudge histograms.

Bug: 1105021
Change-Id: I4b26566a69b7235b15ac0c821a736f898835adea
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3593965


Reviewed-by: Andrew Xu <andrewxu@chromium.org>
Reviewed-by: James Cook <jamescook@chromium.org>
Reviewed-by: Weilun Shi <sweilun@chromium.org>
Commit-Queue: Yulun Wu <yulunwu@chromium.org>
Cr-Commit-Position: refs/heads/main@{#995410}