perf: only redraw for CurSearch when it is currently in use

The check in redraw_for_cursorline() is not needed because VALID_VIRTCOL
is always cleared when the cursor moves to another line, so the check in
redraw_for_cursorcolumn() is enough.

src/nvim/search.c

@@ -6017,3 +6017,9 @@ bool search_was_last_used(void)
 {
   return last_idx == 0;
 }
+
+/// @return  true if 'hlsearch' highlight is currently in use.
+bool using_hlsearch(void)
+{
+  return spats[last_idx].pat != NULL && p_hls && !no_hlsearch;
+}