patch 8.0.1118: FEAT_WINDOWS adds a lot of #ifdefs

Problem:    FEAT_WINDOWS adds a lot of #ifdefs while it is nearly always
            enabled and only adds 7% to the binary size of the tiny build.
Solution:   Graduate FEAT_WINDOWS.
diff --git a/src/fold.c b/src/fold.c
index f8abe22..bc79acc 100644
--- a/src/fold.c
+++ b/src/fold.c
@@ -95,7 +95,7 @@
 
 /* Exported folding functions. {{{1 */
 /* copyFoldingState() {{{2 */
-#if defined(FEAT_WINDOWS) || defined(PROTO)
+
 /*
  * Copy that folding state from window "wp_from" to window "wp_to".
  */
@@ -106,7 +106,6 @@
     wp_to->w_foldinvalid = wp_from->w_foldinvalid;
     cloneFoldGrowArray(&wp_from->w_folds, &wp_to->w_folds);
 }
-#endif
 
 /* hasAnyFolding() {{{2 */
 /*