Fix double divider in Apps & notifications page

- The second divider is shown after we set a background to the pinned
  header.
- Fix it by simply hiding the pinned header instead of its inner views.

Fixes: 133231218
Test: robotest, visual
Change-Id: I53add6f01930299425ce96d23350f9f066e85145

tests/robotests/src/com/android/settings/SettingsPreferenceFragmentTest.java

@@ -29,6 +29,7 @@ import static org.mockito.Mockito.when;
 import android.content.Context;
 import android.os.Bundle;
 import android.view.View;
+import android.widget.FrameLayout;
 
 import androidx.fragment.app.FragmentActivity;
 import androidx.preference.Preference;
@@ -187,6 +188,24 @@ public class SettingsPreferenceFragmentTest {
         verify(workOnlyCategory).setVisible(false);
     }
 
+    @Test
+    public void showPinnedHeader_shouldBeVisible() {
+        mFragment.mPinnedHeaderFrameLayout = new FrameLayout(mContext);
+
+        mFragment.showPinnedHeader(true);
+
+        assertThat(mFragment.mPinnedHeaderFrameLayout.getVisibility()).isEqualTo(View.VISIBLE);
+    }
+
+    @Test
+    public void hidePinnedHeader_shouldBeInvisible() {
+        mFragment.mPinnedHeaderFrameLayout = new FrameLayout(mContext);
+
+        mFragment.showPinnedHeader(false);
+
+        assertThat(mFragment.mPinnedHeaderFrameLayout.getVisibility()).isEqualTo(View.INVISIBLE);
+    }
+
     public static class TestFragment extends SettingsPreferenceFragment {
 
         @Override