patch 8.1.2205: sign entry structure has confusing name

Problem:    Sign entry structure has confusing name.
Solution:   Rename signlist_T to sign_entry_T and prefix se_ to the fields.

src/version.c

@@ -741,6 +741,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2205,
 /**/
     2204,
 /**/