Enable flag to hide half-swipe shelf

Bug: 171817112
Test: visual - shelf that shows on notif half-swipe gone by default
Test: gradle - first, build with sysuiTestDebug variant and SystemUITests config. Then run

adb shell am instrument -w -e class com.android.systemui.statusbar.notification.row.NotificationMenuRowTest com.android.systemui.tests

Change-Id: I1b359e73d2ce9cff7cdbf367ce7002e5710d5946