Fix autofill wallet metadata notification type.

Autofill wallet metadata notification identifier should be
"WALLET_METADATA" instead of "AUTOFILL_WALLET_METADATA" on the client
side to match the server side sync. The server uses the name of the
protobuf WalletMetadataSpecifics to derive the identifier. This affects
only wallet metadata update notifications.

BUG=593546

Review URL: https://codereview.chromium.org/1806853006

Cr-Commit-Position: refs/heads/master@{#381828}

sync/syncable/model_type.cc

@@ -60,7 +60,7 @@ const ModelTypeInfo kModelTypeInfoMap[] = {
     {AUTOFILL_WALLET_DATA, "AUTOFILL_WALLET", "autofill_wallet",
      "Autofill Wallet", sync_pb::EntitySpecifics::kAutofillWalletFieldNumber,
      34},
-    {AUTOFILL_WALLET_METADATA, "AUTOFILL_WALLET_METADATA",
+    {AUTOFILL_WALLET_METADATA, "WALLET_METADATA",
      "autofill_wallet_metadata", "Autofill Wallet Metadata",
      sync_pb::EntitySpecifics::kWalletMetadataFieldNumber, 35},
     {THEMES, "THEME", "themes", "Themes",