Remove default threadpool (#264)

It's not used for anything and threadpools can be created manually.

src/cute_app.cpp

@@ -365,11 +365,6 @@ CF_Result cf_make_app(const char* window_title, CF_DisplayID display_id, int x,
 		}
 	}
 
-	int num_threads_to_spawn = cf_core_count() - 1;
-	if (num_threads_to_spawn) {
-		app->threadpool = cf_make_threadpool(num_threads_to_spawn);
-	}
-
 	CF_Result err = cf_fs_init(argv0);
 	if (cf_is_error(err)) {
 		CF_ASSERT(0);
@@ -402,7 +397,6 @@ void cf_destroy_app()
 	if (app->device) SDL_ReleaseWindowFromGPUDevice(app->device, app->window);
 	SDL_DestroyWindow(app->window);
 	if (app->device) SDL_DestroyGPUDevice(app->device);
-	destroy_threadpool(app->threadpool);
 	SDL_Quit();
 	cs_shutdown();
 	CF_Image* easy_sprites = app->easy_sprites.items();

src/internal/cute_app_internal.h

@@ -72,7 +72,6 @@ struct CF_App
 	SDL_GPUDevice* device = NULL;
 	cs_context_t* cute_sound = NULL;
 	bool spawned_mix_thread = false;
-	CF_Threadpool* threadpool = NULL;
 	void (*on_shader_changed_fn)(const char* path, void* udata) = NULL;
 	void* on_shader_changed_udata = NULL;
 	bool shader_directory_set = false;