internal/restorable: remove ImageTypeVolatile

[hajimehoshi]

Operating System

• Windows
• macOS
• Linux
• FreeBSD
• OpenBSD
• Android
• iOS
• Nintendo Switch
• PlayStation 5
• Xbox
• Web Browsers

What feature would you like to be added?

Now we have Hint which is for optimization when overwriting some regions on a target texture, an image which is cleared every frame should no longer be stale. Thus, we don't need a notion of being volatile. In order to simplify the code, let's try to remove this.

Why is this needed?

To simplify the code.

[hajimehoshi]

an image which is cleared every frame should no longer be stale

Unfortunately this is not true when too many draw calls happen on the same image.