patch 8.2.1422: the Mac GUI implementation is outdated

Problem:    The Mac GUI implementation is outdated and probably doesn't even
            work.
Solution:   Remove the Mac GUI code.  The MacVim project provides the
            supported Vim GUI version.
diff --git a/src/os_mac_conv.c b/src/os_mac_conv.c
index 6c52e7d..3daf74a 100644
--- a/src/os_mac_conv.c
+++ b/src/os_mac_conv.c
@@ -17,7 +17,7 @@
 
 #include "vim.h"
 
-#if !defined(FEAT_GUI_MAC) && !defined(PROTO)
+#if !defined(PROTO)
 # include <CoreServices/CoreServices.h>
 #endif