Revert "Avoid adding transparency to Shelf Background View"

This reverts commit f7e83965.

Reason for revert: Regression (b/425383239). ag/33919549 already fixes the original bug b/420181235

Bug: 420181235
Bug: 425383239
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:afb2fe0be245322d1c4a4881ee808c8827582bf9)
Merged-In: I55137774d0391967d8037fe2418db0e6a6a41429
Change-Id: I55137774d0391967d8037fe2418db0e6a6a41429