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/DolphinWX/FrameTools.cpp

@@ -96,11 +96,6 @@
 #endif
 #endif
 
-// Resources
-extern "C" {
-#include "DolphinWX/resources/Dolphin.c" // NOLINT: Dolphin icon
-};
-
 class InputConfig;
 class wxFrame;