vulkan: don't hold onto ImageData references after loading an image.

Reduces CPU memory usage.

src/modules/graphics/vulkan/Texture.cpp

@@ -41,6 +41,10 @@ Texture::Texture(love::graphics::Graphics *gfx, const Settings &settings, const
 		slices = *data;
 
 	loadVolatile();
+
+	// ImageData is referenced by the first loadVolatile call, but we don't
+	// hang on to it after that so we can save memory.
+	slices.clear();
 }
 
 bool Texture::loadVolatile()