Disable toolbar title of screen lock pages

After applying collapsing toolbar in the Settings app, the toolbar title
will be shown in every subsetting pages. However some pages in the
security category don't need the title, like set screen lock page and
lock screen page. This CL is to disable these titles through overriding
isToolbarEnabled method.

Bug: 176883575
Test: manual test and visual verified
1) Navigate to Settings -> Security -> Screen lock ->
Pattern/PIN/Password
2) Observe and check if there is a duplicated title.

Change-Id: I6dfa4fbe1b5e2ac3582804ba1e125196f3bdba6c

src/com/android/settings/password/ConfirmDeviceCredentialBaseActivity.java

@@ -176,6 +176,11 @@ public abstract class ConfirmDeviceCredentialBaseActivity extends SettingsActivi
         }
     }
 
+    @Override
+    protected boolean isToolbarEnabled() {
+        return false;
+    }
+
     public void prepareEnterAnimation() {
         getFragment().prepareEnterAnimation();
     }