Migrate ENABLE_APP_PAIRS flag to aconfig

Fixes: 303323964
Flag: com.android.wm.shell.Flags.FLAG_ENABLE_APP_PAIRS
Test: Unit tests still run correctly
Change-Id: I617c699746492c9c0d131a28791d984afbbdda4d

src/com/android/launcher3/config/FeatureFlags.java

@@ -274,11 +274,14 @@ public final class FeatureFlags {
                     + " locked. Enabling this causes a 1-time movement of certain SharedPreferences"
                     + " data. Improves startup latency.");
 
-    // TODO(Block 18): Clean up flags
+    // Aconfig migration complete for ENABLE_APP_PAIRS.
     public static final BooleanFlag ENABLE_APP_PAIRS = getDebugFlag(274189428,
             "ENABLE_APP_PAIRS", DISABLED,
             "Enables the ability to create and save app pairs on the Home screen for easy"
                     + " split screen launching.");
+    public static boolean enableAppPairs() {
+        return ENABLE_APP_PAIRS.get() || com.android.wm.shell.Flags.enableAppPairs();
+    }
 
     // TODO(Block 19): Clean up flags
     public static final BooleanFlag SCROLL_TOP_TO_RESET = getReleaseFlag(270395177,