clientupdate: remove TS_NOLAUNCH and GUI restart hacks from autoupdate

We've fixed the underlying issue in github.com/tailscale/corp/issues/13998.

Fixes #10513

Signed-off-by: Aaron Klotz <aaron@tailscale.com>

clientupdate/clientupdate_windows.go

@@ -7,14 +7,6 @@
 package clientupdate
 
 import (
-	"errors"
-	"fmt"
-	"os/exec"
-	"os/user"
-	"path/filepath"
-	"syscall"
-	"unsafe"
-
 	"golang.org/x/sys/windows"
 	"tailscale.com/util/winutil/authenticode"
 )
@@ -22,7 +14,6 @@ import (
 func init() {
 	markTempFileFunc = markTempFileWindows
 	verifyAuthenticode = verifyTailscale
-	launchTailscaleAsWinGUIUser = launchTailscaleAsGUIUser
 }
 
 func markTempFileWindows(name string) error {
@@ -35,50 +26,3 @@ const certSubjectTailscale = "Tailscale Inc."
 func verifyTailscale(path string) error {
 	return authenticode.Verify(path, certSubjectTailscale)
 }
-
-func launchTailscaleAsGUIUser(exePath string) error {
-	exePath = filepath.Join(filepath.Dir(exePath), "tailscale-ipn.exe")
-
-	var token windows.Token
-	if u, err := user.Current(); err == nil && u.Name == "SYSTEM" {
-		sessionID, err := wtsGetActiveSessionID()
-		if err != nil {
-			return fmt.Errorf("wtsGetActiveSessionID(): %w", err)
-		}
-		if err := windows.WTSQueryUserToken(sessionID, &token); err != nil {
-			return fmt.Errorf("WTSQueryUserToken (0x%x): %w", sessionID, err)
-		}
-		defer token.Close()
-	}
-
-	cmd := exec.Command(exePath)
-	cmd.SysProcAttr = &syscall.SysProcAttr{
-		Token:      syscall.Token(token),
-		HideWindow: true,
-	}
-	return cmd.Start()
-}
-
-func wtsGetActiveSessionID() (uint32, error) {
-	var (
-		sessionInfo *windows.WTS_SESSION_INFO
-		count       uint32 = 0
-	)
-
-	const WTS_CURRENT_SERVER_HANDLE = 0
-	if err := windows.WTSEnumerateSessions(WTS_CURRENT_SERVER_HANDLE, 0, 1, &sessionInfo, &count); err != nil {
-		return 0, fmt.Errorf("WTSEnumerateSessions: %w", err)
-	}
-	defer windows.WTSFreeMemory(uintptr(unsafe.Pointer(sessionInfo)))
-
-	current := unsafe.Pointer(sessionInfo)
-	for i := uint32(0); i < count; i++ {
-		session := (*windows.WTS_SESSION_INFO)(current)
-		if session.State == windows.WTSActive {
-			return session.SessionID, nil
-		}
-		current = unsafe.Add(current, unsafe.Sizeof(windows.WTS_SESSION_INFO{}))
-	}
-
-	return 0, errors.New("no active desktop sessions found")
-}