Fix build issues with upstream ifdef for macOS clipboard

Fix incorrect ifdef from upstream Vim as part of gui_mac.c removal.

Author: ychin

src/os_macosx.m

@@ -33,7 +33,7 @@
  * gui_mac.c are used then.  TODO: remove those instead?
  * But for MacVim we do need these ones.
  */
-#if defined(FEAT_CLIPBOARD) && (!defined(FEAT_GUI_ENABLED))
+#if defined(FEAT_CLIPBOARD)
 
 /* Used to identify clipboard data copied from Vim. */