docs: Remove Doxygen \brief tags.

Doxygen and the wiki bridge don't need them; they'll both just use the first
line/sentence instead.

Fixes #8446.

include/SDL3/SDL_render.h

@@ -22,7 +22,7 @@
 /**
  *  \file SDL_render.h
  *
- *  \brief Header file for SDL 2D rendering functions.
+ *  Header file for SDL 2D rendering functions.
  *
  *  This API supports the following features:
  *      * single pixel points