Merge "Remove PROTOTYPE_APP_CLOSE feature flag and associated code." into sc-v2-dev am: 9b85616119 am: 470c4ffe3b

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

Change-Id: I4cf8275faf7a55e3b24aa24175599d32b5bd2098