Remove unnecessary DebugSettingsActivity, use fragment directly

This CL must be checked in together with I1db2e848ab.

Bug: 16522808
Change-Id: I08a1b0c300c504def609cbb53462d215d1ead15c
diff --git a/java/res/xml/prefs.xml b/java/res/xml/prefs.xml
index 550e71a..6febb31 100644
--- a/java/res/xml/prefs.xml
+++ b/java/res/xml/prefs.xml
@@ -199,6 +199,7 @@
             android:defaultValue="true"
             android:persistent="true" />
         <PreferenceScreen
+            android:fragment="com.android.inputmethod.latin.settings.DebugSettings"
             android:key="screen_debug"
             android:title="Debug settings"
             android:defaultValue="false"
diff --git a/java/res/xml/prefs_for_debug.xml b/java/res/xml/prefs_screen_debug.xml
similarity index 100%
rename from java/res/xml/prefs_for_debug.xml
rename to java/res/xml/prefs_screen_debug.xml