patch 8.2.3987: error messages are spread out

Problem:    Error messages are spread out.
Solution:   Move more error messages to errors.h.
diff --git a/src/if_xcmdsrv.c b/src/if_xcmdsrv.c
index 6e653c5..81a4d9d 100644
--- a/src/if_xcmdsrv.c
+++ b/src/if_xcmdsrv.c
@@ -720,7 +720,7 @@
 
     sscanf((char *)str, "0x%x", &id);
     if (id == None)
-	semsg(_("E573: Invalid server id used: %s"), str);
+	semsg(_(e_invalid_server_id_used_str), str);
 
     return (Window)id;
 }