SDL_endian.h: remove aarch64 asm.

The asm has been reported broken in at least optimized Apple M1 builds;
and besides, the compiler builtins have precedence over the asm anyway.

Closes https://github.com/libsdl-org/SDL/issues/3943

include/SDL_endian.h

@@ -135,13 +135,6 @@ SDL_Swap16(Uint16 x)
   __asm__("rlwimi %0,%2,8,16,23": "=&r"(result):"0"(x >> 8), "r"(x));
     return (Uint16)result;
 }
-#elif defined(__aarch64__)
-SDL_FORCE_INLINE Uint16
-SDL_Swap16(Uint16 x)
-{
-  __asm__("rev16 %w1, %w0" : "=r"(x) : "r"(x));
-  return x;
-}
 #elif (defined(__m68k__) && !defined(__mcoldfire__))
 SDL_FORCE_INLINE Uint16
 SDL_Swap16(Uint16 x)
@@ -193,13 +186,6 @@ SDL_Swap32(Uint32 x)
   __asm__("rlwimi %0,%2,24,0,7"  : "=&r"(result): "0" (result), "r"(x));
     return result;
 }
-#elif defined(__aarch64__)
-SDL_FORCE_INLINE Uint32
-SDL_Swap32(Uint32 x)
-{
-  __asm__("rev %w1, %w0": "=r"(x):"r"(x));
-  return x;
-}
 #elif (defined(__m68k__) && !defined(__mcoldfire__))
 SDL_FORCE_INLINE Uint32
 SDL_Swap32(Uint32 x)