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/sign.c b/src/sign.c
index f3a1f9d..71f21b0 100644
--- a/src/sign.c
+++ b/src/sign.c
@@ -496,7 +496,7 @@
 	    break;
 
 	if (sign->se_lnum == lnum
-# ifdef FEAT_TEXT_PROP
+# ifdef FEAT_PROP_POPUP
 		&& sign_group_for_window(sign, wp)
 # endif
 		)
@@ -2656,7 +2656,7 @@
 {
     sign_entry_T *sign = wp->w_buffer->b_signlist;
 
-# ifdef FEAT_TEXT_PROP
+# ifdef FEAT_PROP_POPUP
     while (sign != NULL && !sign_group_for_window(sign, wp))
 	sign = sign->se_next;
 # endif