pkg/system: remove unused HasWin32KSupport()

This was added in 194eaa5c0f843257e66b68bd735786308a9d93b2 to check image
compatibility based on Platform.Features;

    // For now, hard code that all base images except nanoserver depend on win32k support
    if imageData.Name != "nanoserver" {
        imageData.OSFeatures = append(imageData.OSFeatures, "win32k")
    }

But no longer used since 1f59bc8c03df18686b93a0cd619cf2c55cbcf421 and
d231260868507174d60ff58b18b14fa5bc2d5b66

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

pkg/system/syscall_windows.go

@@ -4,25 +4,18 @@ import (
 	"unsafe"
 
 	"github.com/sirupsen/logrus"
-	"golang.org/x/sys/windows"
 )
 
 const (
 	// Deprecated: use github.com/docker/pkg/idtools.SeTakeOwnershipPrivilege
 	SeTakeOwnershipPrivilege = "SeTakeOwnershipPrivilege"
-)
-
-const (
 	// Deprecated: use github.com/docker/pkg/idtools.ContainerAdministratorSidString
 	ContainerAdministratorSidString = "S-1-5-93-2-1"
 	// Deprecated: use github.com/docker/pkg/idtools.ContainerUserSidString
 	ContainerUserSidString = "S-1-5-93-2-2"
 )
 
-var (
-	ntuserApiset      = windows.NewLazyDLL("ext-ms-win-ntuser-window-l1-1-0")
-	procGetVersionExW = modkernel32.NewProc("GetVersionExW")
-)
+var procGetVersionExW = modkernel32.NewProc("GetVersionExW")
 
 // https://docs.microsoft.com/en-us/windows/win32/api/winnt/ns-winnt-osversioninfoexa
 // TODO: use golang.org/x/sys/windows.OsVersionInfoEx (needs OSVersionInfoSize to be exported)
@@ -54,12 +47,3 @@ func IsWindowsClient() bool {
 	const verNTWorkstation = 0x00000001 // VER_NT_WORKSTATION
 	return osviex.ProductType == verNTWorkstation
 }
-
-// HasWin32KSupport determines whether containers that depend on win32k can
-// run on this machine. Win32k is the driver used to implement windowing.
-func HasWin32KSupport() bool {
-	// For now, check for ntuser API support on the host. In the future, a host
-	// may support win32k in containers even if the host does not support ntuser
-	// APIs.
-	return ntuserApiset.Load() == nil
-}

pkg/system/syscall_windows_test.go

@@ -1,9 +0,0 @@
-package system // import "github.com/docker/docker/pkg/system"
-
-import "testing"
-
-func TestHasWin32KSupport(t *testing.T) {
-	s := HasWin32KSupport() // make sure this doesn't panic
-
-	t.Logf("win32k: %v", s) // will be different on different platforms -- informative only
-}