time: unconditionally use RegLoadMUIString on Windows

RegLoadMUIString is supported on Windows Vista and later, so this
should be safe to do unconditionally.

While here, also unconditionally use GetDynamicTimeZoneInformation
in syscall/windows/registry tests, since it's also supported on Windows
Vista and later.

Change-Id: Ifa32a81f4727d4810f2b9ccc814aa77a43513e59
Reviewed-on: https://go-review.googlesource.com/c/go/+/527595
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>
Reviewed-by: Heschi Kreinick <heschi@google.com>
Run-TryBot: Quim Muntal <quimmuntal@gmail.com>

src/internal/syscall/windows/registry/registry_test.go

@@ -599,12 +599,6 @@ func TestInvalidValues(t *testing.T) {
 }
 
 func TestGetMUIStringValue(t *testing.T) {
-	if err := registry.LoadRegLoadMUIString(); err != nil {
-		t.Skip("regLoadMUIString not supported; skipping")
-	}
-	if err := procGetDynamicTimeZoneInformation.Find(); err != nil {
-		t.Skipf("%s not supported; skipping", procGetDynamicTimeZoneInformation.Name)
-	}
 	var dtzi DynamicTimezoneinformation
 	if _, err := GetDynamicTimeZoneInformation(&dtzi); err != nil {
 		t.Fatal(err)

src/internal/syscall/windows/registry/syscall.go

@@ -17,10 +17,6 @@ const (
 	_ERROR_NO_MORE_ITEMS syscall.Errno = 259
 )
 
-func LoadRegLoadMUIString() error {
-	return procRegLoadMUIStringW.Find()
-}
-
 //sys	regCreateKeyEx(key syscall.Handle, subkey *uint16, reserved uint32, class *uint16, options uint32, desired uint32, sa *syscall.SecurityAttributes, result *syscall.Handle, disposition *uint32) (regerrno error) = advapi32.RegCreateKeyExW
 //sys	regDeleteKey(key syscall.Handle, subkey *uint16) (regerrno error) = advapi32.RegDeleteKeyW
 //sys	regSetValueEx(key syscall.Handle, valueName *uint16, reserved uint32, vtype uint32, buf *byte, bufsize uint32) (regerrno error) = advapi32.RegSetValueExW

src/internal/syscall/windows/registry/value.go

@@ -115,9 +115,6 @@ func (k Key) GetStringValue(name string) (val string, valtype uint32, err error)
 // the specified value name associated with an open key k.
 // If the value name doesn't exist or the localized string value
 // can't be resolved, GetMUIStringValue returns ErrNotExist.
-// GetMUIStringValue panics if the system doesn't support
-// regLoadMUIString; use LoadRegLoadMUIString to check if
-// regLoadMUIString is supported before calling this function.
 func (k Key) GetMUIStringValue(name string) (string, error) {
 	pname, err := syscall.UTF16PtrFromString(name)
 	if err != nil {

src/time/zoneinfo_windows.go

@@ -20,8 +20,8 @@ var platformZoneSources []string // none: Windows uses system calls instead
 // time apply to all previous and future years as well.
 
 // matchZoneKey checks if stdname and dstname match the corresponding key
-// values "MUI_Std" and MUI_Dlt" or "Std" and "Dlt" (the latter down-level
+// values "MUI_Std" and MUI_Dlt" or "Std" and "Dlt" in the kname key stored
-// from Vista) in the kname key stored under the open registry key zones.
+// under the open registry key zones.
 func matchZoneKey(zones registry.Key, kname string, stdname, dstname string) (matched bool, err2 error) {
 	k, err := registry.OpenKey(zones, kname, registry.READ)
 	if err != nil {
@@ -30,13 +30,11 @@ func matchZoneKey(zones registry.Key, kname string, stdname, dstname string) (ma
 	defer k.Close()
 
 	var std, dlt string
-	if err = registry.LoadRegLoadMUIString(); err == nil {
 	// Try MUI_Std and MUI_Dlt first, fallback to Std and Dlt if *any* error occurs
 	std, err = k.GetMUIStringValue("MUI_Std")
 	if err == nil {
 		dlt, err = k.GetMUIStringValue("MUI_Dlt")
 	}
-	}
 	if err != nil { // Fallback to Std and Dlt
 		if std, _, err = k.GetStringValue("Std"); err != nil {
 			return false, err

src/time/zoneinfo_windows_test.go

@@ -45,13 +45,11 @@ func TestToEnglishName(t *testing.T) {
 	defer k.Close()
 
 	var std, dlt string
-	if err = registry.LoadRegLoadMUIString(); err == nil {
 	// Try MUI_Std and MUI_Dlt first, fallback to Std and Dlt if *any* error occurs
 	std, err = k.GetMUIStringValue("MUI_Std")
 	if err == nil {
 		dlt, err = k.GetMUIStringValue("MUI_Dlt")
 	}
-	}
 	if err != nil { // Fallback to Std and Dlt
 		if std, _, err = k.GetStringValue("Std"); err != nil {
 			t.Fatalf("cannot read CEST Std registry key: %s", err)