block/file-posix: Drop ifdef for macOS versions older than 12.0

macOS versions older than 12.0 are no longer supported.

docs/about/build-platforms.rst says:
> Support for the previous major version will be dropped 2 years after
> the new major version is released or when the vendor itself drops
> support, whichever comes first.

macOS 12.0 was released 2021:
https://www.apple.com/newsroom/2021/10/macos-monterey-is-now-available/

Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20240629-macos-v1-3-6e70a6b700a0@daynix.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>

block/file-posix.c

@@ -3929,11 +3929,6 @@ BlockDriver bdrv_file = {
 static kern_return_t GetBSDPath(io_iterator_t mediaIterator, char *bsdPath,
                                 CFIndex maxPathSize, int flags);
 
-#if !defined(MAC_OS_VERSION_12_0) \
-    || (MAC_OS_X_VERSION_MIN_REQUIRED < MAC_OS_VERSION_12_0)
-#define IOMainPort IOMasterPort
-#endif
-
 static char *FindEjectableOpticalMedia(io_iterator_t *mediaIterator)
 {
     kern_return_t kernResult = KERN_FAILURE;