yuzu: Drop SDL2 and Qt frontend Vulkan requirements

Create Vulkan instances and surfaces from the Vulkan backend.

src/yuzu_tester/emu_window/emu_window_sdl2_hide.cpp

@@ -116,10 +116,6 @@ bool EmuWindow_SDL2_Hide::IsShown() const {
     return false;
 }
 
-void EmuWindow_SDL2_Hide::RetrieveVulkanHandlers(void*, void*, void*) const {
-    UNREACHABLE();
-}
-
 class SDLGLContext : public Core::Frontend::GraphicsContext {
 public:
     explicit SDLGLContext() {