DolphinWX: Stop using XPM images

Using the XPM format for images has become a maintenance problem because
people don't know how to create them. This commit removes all XPM images
and all C files that contain PNG images. DolphinWX now uses the PNGs
in the Resources folder instead, just like DolphinQt and DolphinQt2 do.

Source/Core/DiscIO/VolumeCommon.cpp

@@ -79,7 +79,7 @@ IVolume::ECountry CountrySwitch(u8 country_code)
 {
 	switch (country_code)
 	{
-		// Region free - Uses European flag as placeholder
+		// Worldwide
 		case 'A':
 			return IVolume::COUNTRY_WORLD;