runtime: fix arm

signal.test binary passes on my phone; should fix builder

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/5694064

src/pkg/runtime/defs_arm_linux.go

@@ -114,7 +114,6 @@ const (
 	ITIMER_VIRTUAL = C.ITIMER_VIRTUAL
 )
 
-type Sigset C.sigset_t
 type Timespec C.struct_timespec
 type Sigaltstack C.struct_sigaltstack
 type Sigcontext C.struct_sigcontext

src/pkg/runtime/defs_linux_arm.h

@@ -69,8 +69,6 @@ enum {
 // Types
 #pragma pack on
 
-typedef uint32 Sigset;
-
 typedef struct Timespec Timespec;
 struct Timespec {
 	int32 tv_sec;