Android: Don't use getEmulationActivity in GCAdapter/Wiimote code

The app context should work just as well as an activity context.

Also moving a hardcoded string to strings.xml.

Source/Android/app/src/main/res/values/strings.xml

@@ -466,6 +466,7 @@ It can efficiently compress both junk data and encrypted Wii data.
     <string name="default_values">Default Values</string>
     <string name="slider_setting_value">%1$d%2$s</string>
     <string name="disc_number">Disc %1$d</string>
+    <string name="replug_gc_adapter">GameCube Adapter couldn\'t be opened. Please re-plug the device.</string>
     <string name="disabled_gc_overlay_notice">GameCube Controller 1 is set to \"None\"</string>
     <string name="ignore_warning_alert_messages">Ignore for this session</string>