all: cleanup unused code, part 2 (#10670)

And enable U1000 check in staticcheck.

Updates #cleanup

Signed-off-by: Andrew Lytvynov <awly@tailscale.com>

safesocket/pipe_windows.go

@@ -10,7 +10,6 @@ import (
 	"fmt"
 	"net"
 	"runtime"
-	"syscall"
 	"time"
 
 	"github.com/tailscale/go-winio"
@@ -26,13 +25,6 @@ func connect(path string) (net.Conn, error) {
 	return winio.DialPipeAccessImpLevel(ctx, path, windows.GENERIC_READ|windows.GENERIC_WRITE, winio.PipeImpLevelIdentification)
 }
 
-func setFlags(network, address string, c syscall.RawConn) error {
-	return c.Control(func(fd uintptr) {
-		syscall.SetsockoptInt(syscall.Handle(fd), syscall.SOL_SOCKET,
-			syscall.SO_REUSEADDR, 1)
-	})
-}
-
 // windowsSDDL is the Security Descriptor set on the namedpipe.
 // It provides read/write access to all users and the local system.
 // It is a var for testing, do not change this value.