ImageData: remove automatic mutex locks.

src/modules/graphics/GraphicsReadback.cpp

@@ -192,6 +192,7 @@ GraphicsReadback::Status GraphicsReadback::readbackBuffer(Buffer *buffer, size_t
 
 		if (imageData.get())
 		{
+			// Always lock the mutex since the user can't know when to do it.
 			love::thread::Lock lock(imageData->getMutex());
 
 			if (imageData->getWidth() != rect.w)

src/modules/graphics/Texture.cpp

@@ -451,12 +451,6 @@ void Texture::drawLayer(Graphics *gfx, int layer, Quad *q, const Matrix4 &m)
 
 void Texture::uploadImageData(love::image::ImageDataBase *d, int level, int slice, int x, int y)
 {
-	love::image::ImageData *id = dynamic_cast<love::image::ImageData *>(d);
-
-	love::thread::EmptyLock lock;
-	if (id != nullptr)
-		lock.setLock(id->getMutex());
-
 	Rect rect = {x, y, d->getWidth(), d->getHeight()};
 	uploadByteData(d->getData(), d->getSize(), level, slice, rect);
 }

src/modules/graphics/opengl/GraphicsReadback.cpp

@@ -68,8 +68,6 @@ GraphicsReadback::GraphicsReadback(love::graphics::Graphics *gfx, ReadbackMethod
 	{
 		void *dest = prepareReadbackDest(size);
 
-		love::thread::Lock lock(imageData->getMutex());
-
 		// Direct readback without copying avoids the need for a staging buffer,
 		// and lowers the system requirements of immediate RT readback.
 		Texture *t = (Texture *) texture;