patch 8.2.3986: error messages are spread out

Problem:    Error messages are spread out.
Solution:   Move more error messages to errors.h.
diff --git a/src/help.c b/src/help.c
index a356e7f..77b2205 100644
--- a/src/help.c
+++ b/src/help.c
@@ -60,7 +60,7 @@
 
 	if (eap->forceit && *arg == NUL && !curbuf->b_help)
 	{
-	    emsg(_("E478: Don't panic!"));
+	    emsg(_(e_dont_panic));
 	    return;
 	}