Migrate predictive back flags to aconfig

Bug: 309545085
Flag: ACONFIG com.android.systemui.predictive_back_sysui DISABLED
Flag: ACONFIG com.android.systemui.predictive_back_animate_shade DISABLED
Flag: ACONFIG com.android.systemui.shade_allow_back_gesture DISABLED
Flag: ACONFIG com.android.systemui.predictive_back_bouncer_anim DISABLED
Test: atest BackActionInteractorTest
Test: atest CentralSurfacesImplTest
Test: atest NotificationPanelViewControllerBaseTest
Test: atest StatusBarKeyguardViewManagerTest
Test: Manual, i.e. testing build on device and verifying behaviour of flagged features
Change-Id: I940233b69957819445cd3efb46ee598a3414e3e8