SDL: Revert "Added SDL_FLIP_DIAGONAL"

From fde420a6453ca67cc2f99d853937c73c9f175530 Mon Sep 17 00:00:00 2001
From: Sam Lantinga <[EMAIL REDACTED]>
Date: Sun, 10 Mar 2024 15:20:36 -0700
Subject: [PATCH] Revert "Added SDL_FLIP_DIAGONAL"

This reverts commit b9ab3269823ea329757aada3a20ef97abf1a9f6d.

@rainerdeyke pointed out:
"This commit is incorrect. Flipping both horizontally and vertically is not equivalent to flipping diagonally."
---
 include/SDL3/SDL_surface.h | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/include/SDL3/SDL_surface.h b/include/SDL3/SDL_surface.h
index aac7f4548f69..d42604fad69e 100644
--- a/include/SDL3/SDL_surface.h
+++ b/include/SDL3/SDL_surface.h
@@ -80,10 +80,9 @@ typedef enum
  */
 typedef enum
 {
-    SDL_FLIP_NONE       = 0x00,     /**< Do not flip */
-    SDL_FLIP_HORIZONTAL = 0x01,     /**< flip horizontally */
-    SDL_FLIP_VERTICAL   = 0x02,     /**< flip vertically */
-    SDL_FLIP_DIAGONAL   = 0x03,     /**< flip diagonally (both horizontally and vertically) */
+    SDL_FLIP_NONE,          /**< Do not flip */
+    SDL_FLIP_HORIZONTAL,    /**< flip horizontally */
+    SDL_FLIP_VERTICAL       /**< flip vertically */
 } SDL_FlipMode;
 
 /**