patch 8.2.1460: error messages are spread out

Problem:    Error messages are spread out.
Solution:   Move more messages into errors.h.
diff --git a/src/eval.c b/src/eval.c
index 984835b..70d5b34 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -858,7 +858,7 @@
     v = find_var(lp->ll_name, (flags & GLV_READ_ONLY) ? NULL : &ht,
 						      flags & GLV_NO_AUTOLOAD);
     if (v == NULL && !quiet)
-	semsg(_(e_undefvar), lp->ll_name);
+	semsg(_(e_undefined_variable_str), lp->ll_name);
     *p = cc;
     if (v == NULL)
 	return NULL;