patch 8.2.4008: error messages are spread out

Problem:    Error messages are spread out.
Solution:   Move more error messages to errors.h.
diff --git a/src/evalvars.c b/src/evalvars.c
index ce27cee..462cdc2 100644
--- a/src/evalvars.c
+++ b/src/evalvars.c
@@ -1968,7 +1968,7 @@
 
     if (recurse >= DICT_MAXNEST)
     {
-	emsg(_("E743: variable nested too deep for (un)lock"));
+	emsg(_(e_variable_nested_too_deep_for_unlock));
 	return;
     }
     if (deep == 0)