runtime: remove unused type sigtabtt

The type sigtabtt was introduced by an automated tool in
https://golang.org/cl/167550043. It was the Go version of the C type
SigTab. However, when the C code using SigTab was converted to Go in
https://golang.org/cl/168500044 it was rewritten to use a different Go
type, sigTabT, rather than sigtabtt (the difference being that sigTabT
uses string where sigtabtt uses *int8 from the C type char*). So this is
just a dreg from the conversion that was never actually used.

Change-Id: I2ec6eb4b25613bf5e5ad1dbba1f4b5ff20f80f55
Reviewed-on: https://go-review.googlesource.com/27691
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/runtime/runtime2.go

@@ -575,11 +575,6 @@ const (
 	_LockInternal = 2
 )
 
-type sigtabtt struct {
-	flags int32
-	name  *int8
-}
-
 const (
 	_SigNotify   = 1 << iota // let signal.Notify have signal, even if from kernel
 	_SigKill                 // if signal.Notify doesn't take it, exit quietly