Clean up before making all setting page render edge-to-edge

These classes are casting view to LinearLayout unnecessarily. Later we
might change the root view away from LinearLayout. The cast will cause
crash.

Bug: 132182711
Test: go through SUW.
Change-Id: Iea31882f8edea0c87ef8e95b4da9b6bffa8ea7d0

src/com/android/settings/EncryptionInterstitial.java

@@ -84,8 +84,7 @@ public class EncryptionInterstitial extends SettingsActivity {
     @Override
     protected void onCreate(Bundle savedInstance) {
         super.onCreate(savedInstance);
-        LinearLayout layout = (LinearLayout) findViewById(R.id.content_parent);
-        layout.setFitsSystemWindows(false);
+        findViewById(R.id.content_parent).setFitsSystemWindows(false);
     }
 
     public static class EncryptionInterstitialFragment extends InstrumentedFragment {