Merge "Remove PROTOTYPE_APP_CLOSE feature flag and associated code." into sc-v2-dev am: 9b85616119

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/apps/Launcher3/+/16151440

Change-Id: Ie1d4effa0daddbea4f60f693f3e5679fefa19300