Tweak bluetooth text alignment

1. Remove the placeholder summary so it won't show blank summary
2. Update settings_entity_header to make text center_vertical,
so it could align with the icon.

Bug: 71742145
Test: Screenshot
Change-Id: I185114a4e0c8d996f218075a8633e802fabf3c66

tests/robotests/src/com/android/settings/bluetooth/BluetoothDeviceUpdaterTest.java

@@ -95,8 +95,6 @@ public class BluetoothDeviceUpdaterTest {
 
         final Preference preference = mBluetoothDeviceUpdater.mPreferenceMap.get(mBluetoothDevice);
         assertThat(preference).isNotNull();
-        assertThat(preference.getSummary()).isEqualTo(
-                mContext.getString(R.string.summary_placeholder));
         verify(mDevicePreferenceCallback).onDeviceAdded(preference);
     }