Use config changed callback to detect SD insertion/ejection

This saves the GUI from having to manually call SDIO_EventNotify.
With that out of the way, we can let users change the
"Insert SD Card" setting on Android while a game is running.

Source/Android/app/src/main/java/org/dolphinemu/dolphinemu/features/settings/model/BooleanSetting.java

@@ -228,7 +228,6 @@ public enum BooleanSetting implements AbstractBooleanSetting
           MAIN_CPU_THREAD,
           MAIN_ENABLE_CHEATS,
           MAIN_OVERRIDE_REGION_SETTINGS,
-          MAIN_WII_SD_CARD,  // Can actually be changed, but specialized code is required
           MAIN_MMU,
           MAIN_DSP_JIT,
   };