patch 8.0.1236: Mac features are confusing

Problem:    Mac features are confusing.
Solution:   Make feature names more consistent, add "osxdarwin". Rename
            feature flags, cleanup Mac code. (Kazunobu Kuriyama, closes #2178)

src/window.c

@@ -6364,7 +6364,7 @@ vim_FullName(
 	/* something failed; use the file name (truncate when too long) */
 	vim_strncpy(buf, fname, len - 1);
     }
-#if defined(MACOS_CLASSIC) || defined(MSWIN)
+#if defined(MSWIN)
     slash_adjust(buf);
 #endif
     return retval;