runtime: remove redeclared structs to make tests build

struct32 and struct40 structs are already declared, remove them to
make runtime tests build.

Change-Id: I3814f2b850dcb15c4002a3aa22e2a9326e5a5e53
Reviewed-on: https://go-review.googlesource.com/55614Reviewed-by: Martin Möhrmann <moehrmann@google.com>

src/runtime/chan_test.go

@@ -669,11 +669,7 @@ done:
 	<-ready2
 }
 
-type (
-	struct0  struct{}
-	struct32 struct{ a, b, c, d int64 }
-	struct40 struct{ a, b, c, d, e int64 }
-)
+type struct0 struct{}
 
 func BenchmarkMakeChan(b *testing.B) {
 	b.Run("Byte", func(b *testing.B) {