Revert "Do not retain album art in NotificationMediaManager if unused"

This reverts commit 4f6344bab4311d559050911167542c9b1a26718b.

Reason for revert: Droidfood locking bug: b/278672382
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:b20d1951620813e1e361b4436c1d5763f4521ee3)
Merged-In: I9ef9dfeeac4d493c75bdf6cd5d58f344323c60d7
Change-Id: I9ef9dfeeac4d493c75bdf6cd5d58f344323c60d7
3 files changed