Merge DSU joystick driver into SDL_dsujoystick.c

Moved all DSU joystick driver logic from SDL_dsujoystick_driver.c into SDL_dsujoystick.c, removing the separate driver file. Updated SDL_dsujoystick_c.h to remove internal driver declarations and macros now handled in the implementation. Updated VisualC project file to remove the deleted driver source.

Author: danprice142

VisualC/SDL/SDL.vcxproj

@@ -640,7 +640,6 @@
     <ClCompile Include="..\..\src\joystick\SDL_joystick.c" />
     <ClCompile Include="..\..\src\joystick\SDL_steam_virtual_gamepad.c" />
     <ClCompile Include="..\..\src\joystick\dsu\SDL_dsujoystick.c" />
-    <ClCompile Include="..\..\src\joystick\dsu\SDL_dsujoystick_driver.c" />
     <ClCompile Include="..\..\src\joystick\virtual\SDL_virtualjoystick.c" />
     <ClCompile Include="..\..\src\joystick\windows\SDL_dinputjoystick.c" />
     <ClCompile Include="..\..\src\joystick\windows\SDL_rawinputjoystick.c" />