use shadycss externs directly, now only 498 warnings

externs/webcomponents-externs.js

@@ -12,24 +12,6 @@ let HTMLImports = {
 
 window.HTMLImports = HTMLImports;
 
-let ShadyCSS = {
-  /**
-   * @param {!HTMLElement} element
-   * @param {Object=} overrides
-   */
-  applyStyle(element, overrides){},
-  updateStyles(){},
-  /**
-   * @param {!HTMLTemplateElement} template
-   * @param {string} is
-   * @param {string=} extendsElement
-   */
-  prepareTemplate(template, is, extendsElement){},
-  nativeCss: false,
-  nativeShadow: false
-};
-window.ShadyCSS = ShadyCSS;
-
 let ShadyDOM = {
   inUse: false,
   flush(){},