[webview_flutter] Remove non-public API (#487)

ewk_settings_viewport_meta_tag_set() was moved to ewk_settings_product.h in tizen 6.5.
Since this header is non-public, we can no longer use this api.
By default, the viewport meta tag is enabled on mobile and wearable, but it is disabled on TV.
Since webview_flutter_tizen only support the TV profile, it doesn't matter if we don't use this API.

Author: JSUYA

packages/webview_flutter/tizen/src/webview.cc

@@ -347,7 +347,6 @@ void WebView::InitWebView() {
     ewk_cookie_manager_accept_policy_set(
         manager, EWK_COOKIE_ACCEPT_POLICY_NO_THIRD_PARTY);
   }
-  ewk_settings_viewport_meta_tag_set(settings, false);
   EwkInternalApiBinding::GetInstance().settings.ImePanelEnabledSet(settings,
                                                                    true);
   ewk_settings_javascript_enabled_set(settings, true);