Note the removal of the SDL_RENDERER_TARGETTEXTURE flag

Render targets are a core feature of SDL 3.0, so this flag has been removed.

The OpenGL ES renderer still doesn't support them, but we'll deal with that later.

Fixes https://github.com/libsdl-org/SDL/issues/8059

docs/README-migration.md

@@ -698,6 +698,8 @@ which index is the "opengl" or whatnot driver, you can just pass that string dir
 here, now. Passing NULL is the same as passing -1 here in SDL2, to signify you want SDL
 to decide for you.
 
+The SDL_RENDERER_TARGETTEXTURE flag has been removed, all current renderers support target texture functionality.
+
 When a renderer is created, it will automatically set the logical size to the size of
 the window in points. For high DPI displays, this will set up scaling from points to
 pixels. You can disable this scaling with:

include/SDL3/SDL_render.h

@@ -778,10 +778,6 @@ extern DECLSPEC void SDLCALL SDL_UnlockTexture(SDL_Texture *texture);
 /**
  * Set a texture as the current rendering target.
  *
- * Before using this function, you should check the
- * `SDL_RENDERER_TARGETTEXTURE` bit in the flags of SDL_RendererInfo to see if
- * render targets are supported.
- *
  * The default render target is the window for which the renderer was created.
  * To stop rendering to a texture and render to the window again, call this
  * function with a NULL `texture`.