Revert "Revert "Update theme for ChannelPanelActivity""

This reverts commit bbef903b882a93e9e78b5d9f59b71587d2921fc0.

Reason for revert: This CL is fixing notification panel theme issue.

Change-Id: I6bcd8c8f1e8d2f2bd2f7896ebf45d36f67f570b9
diff --git a/AndroidManifest.xml b/AndroidManifest.xml
index 6fe6832..08fbf04 100644
--- a/AndroidManifest.xml
+++ b/AndroidManifest.xml
@@ -3717,7 +3717,7 @@
         <!-- Show channel-level notification settings (channel passed in as extras) -->
         <activity android:name=".notification.app.ChannelPanelActivity"
                   android:label="@string/notification_channel_title"
-                  android:theme="@style/Theme.Panel"
+                  android:theme="@style/Theme.Panel.Material"
                   android:excludeFromRecents="true"
                   android:configChanges="keyboardHidden|screenSize"
                   android:exported="true">