Cleanup keyboard theme switching code

Change-Id: I023769b765d07237b2129d8f1b2a02ffd4c4f09d
diff --git a/java/res/values/config.xml b/java/res/values/config.xml
index 9e962ee..635b216 100644
--- a/java/res/values/config.xml
+++ b/java/res/values/config.xml
@@ -48,7 +48,7 @@
     <integer name="config_keyboard_grid_height">16</integer>
     <integer name="config_double_spaces_turn_into_period_timeout">1100</integer>
     <!-- This configuration is the index of the array {@link KeyboardSwitcher.KEYBOARD_THEMES}. -->
-    <string name="config_default_keyboard_theme_id" translatable="false">5</string>
+    <string name="config_default_keyboard_theme_index" translatable="false">5</string>
     <integer name="config_max_more_keys_column">5</integer>
     <!--
          Configuration for KeyboardView