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/popupwin.c b/src/popupwin.c
index e1c21ac..5385296 100644
--- a/src/popupwin.c
+++ b/src/popupwin.c
@@ -13,7 +13,7 @@
 
 #include "vim.h"
 
-#if defined(FEAT_TEXT_PROP) || defined(PROTO)
+#if defined(FEAT_PROP_POPUP) || defined(PROTO)
 
 typedef struct {
     char	*pp_name;
@@ -3864,4 +3864,4 @@
 	popup_set_title(wp);
 }
 
-#endif // FEAT_TEXT_PROP
+#endif // FEAT_PROP_POPUP