ios: Renamed APIs that referred to "iPhone" to refer to "iOS".

Macros that papered over this difference in SDL2 have been removed for SDL3.

Fixes #9527.

docs/README-ios.md

@@ -222,7 +222,7 @@ Game Center
 
 Game Center integration might require that you break up your main loop in order to yield control back to the system. In other words, instead of running an endless main loop, you run each frame in a callback function, using:
 
-    int SDL_iPhoneSetAnimationCallback(SDL_Window * window, int interval, void (*callback)(void*), void *callbackParam);
+    int SDL_iOSSetAnimationCallback(SDL_Window * window, int interval, void (*callback)(void*), void *callbackParam);
 
 This will set up the given function to be called back on the animation callback, and then you have to return from main() to let the Cocoa event loop run.
 
@@ -244,7 +244,7 @@ e.g.
 
         // Set up the game to run in the window animation callback on iOS
         // so that Game Center and so forth works correctly.
-        SDL_iPhoneSetAnimationCallback(window, 1, ShowFrame, NULL);
+        SDL_iOSSetAnimationCallback(window, 1, ShowFrame, NULL);
     #else
         while ( running ) {
             ShowFrame(0);