patch 8.1.2371: FEAT_TEXT_PROP is a confusing name

Problem:    FEAT_TEXT_PROP is a confusing name.
Solution:   Use FEAT_PROP_POPUP. (Naruhiko Nishino, closes #5291)
diff --git a/src/gui_w32.c b/src/gui_w32.c
index d5dfeff..d094be6 100644
--- a/src/gui_w32.c
+++ b/src/gui_w32.c
@@ -4255,7 +4255,7 @@
 
     wp = gui_mouse_window(FIND_POPUP);
 
-#ifdef FEAT_TEXT_PROP
+#ifdef FEAT_PROP_POPUP
     if (wp != NULL && popup_is_popup(wp))
     {
 	cmdarg_T cap;