patch 8.2.1422: the Mac GUI implementation is outdated

Problem:    The Mac GUI implementation is outdated and probably doesn't even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/vim.h b/src/vim.h
index 1001117..a780ec9 100644
--- a/src/vim.h
+++ b/src/vim.h
@@ -97,14 +97,12 @@
 // Unless made through the Makefile enforce GUI on Mac
 #if defined(MACOS_X) && !defined(HAVE_CONFIG_H)
 # define UNIX
-# define FEAT_GUI_MAC
 #endif
 
 #if defined(FEAT_GUI_MOTIF) \
     || defined(FEAT_GUI_GTK) \
     || defined(FEAT_GUI_ATHENA) \
     || defined(FEAT_GUI_HAIKU) \
-    || defined(FEAT_GUI_MAC) \
     || defined(FEAT_GUI_MSWIN) \
     || defined(FEAT_GUI_PHOTON)
 # define FEAT_GUI_ENABLED  // also defined with NO_X11_INCLUDES
@@ -2144,7 +2142,7 @@
 // been seen at that stage.  But it must be before globals.h, where error_ga
 // is declared.
 #if !defined(MSWIN) && !defined(FEAT_GUI_X11) && !defined(FEAT_GUI_HAIKU) \
-	&& !defined(FEAT_GUI_GTK) && !defined(FEAT_GUI_MAC) && !defined(PROTO)
+	&& !defined(FEAT_GUI_GTK) && !defined(PROTO)
 # define mch_errmsg(str)	fprintf(stderr, "%s", (str))
 # define display_errors()	fflush(stderr)
 # define mch_msg(str)		printf("%s", (str))
@@ -2154,8 +2152,7 @@
 
 # if defined(FEAT_EVAL) \
 	&& (!defined(FEAT_GUI_MSWIN) \
-	     || !(defined(FEAT_MBYTE_IME) || defined(GLOBAL_IME))) \
-	&& !(defined(FEAT_GUI_MAC) && defined(MACOS_CONVERT))
+	     || !(defined(FEAT_MBYTE_IME) || defined(GLOBAL_IME)))
 // Whether IME is supported by im_get_status() defined in mbyte.c.
 // For Win32 GUI it's in gui_w32.c when FEAT_MBYTE_IME or GLOBAL_IME is defined.
 // for Mac it is in gui_mac.c for the GUI or in os_mac_conv.c when
@@ -2166,8 +2163,7 @@
 #if defined(FEAT_XIM) \
 	|| defined(IME_WITHOUT_XIM) \
 	|| (defined(FEAT_GUI_MSWIN) \
-	    && (defined(FEAT_MBYTE_IME) || defined(GLOBAL_IME))) \
-	|| defined(FEAT_GUI_MAC)
+	    && (defined(FEAT_MBYTE_IME) || defined(GLOBAL_IME)))
 // im_set_active() is available
 # define HAVE_INPUT_METHOD
 #endif