syscall: drop fallback to pipe in Pipe on linux/arm

Follow-up for CL 346789

The minimum required Linux kernel version for Go 1.18 will be changed to
2.6.32, see #45964. The pipe2 syscall was added in 2.6.27, so the
fallback to use pipe in Pipe on linux/arm can be removed.

For #45964

Change-Id: I8b18244ca1f849f10e90565b4fef80ce777fef69
Reviewed-on: https://go-review.googlesource.com/c/go/+/347349
Trust: Tobias Klauser <[email protected]>
Run-TryBot: Tobias Klauser <[email protected]>
TryBot-Result: Go Bot <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>

Author: tklauser

src/syscall/syscall_linux_arm.go

@@ -29,11 +29,7 @@ func Pipe(p []int) (err error) {
 		return EINVAL
 	}
 	var pp [2]_C_int
-	// Try pipe2 first for Android O, then try pipe for kernel 2.6.23.
 	err = pipe2(&pp, 0)
-	if err == ENOSYS {
-		err = pipe(&pp)
-	}
 	p[0] = int(pp[0])
 	p[1] = int(pp[1])
 	return