MD WebUI: Delete cr-search-field, simplify CrSearchFieldBehavior

ui/webui/resources/cr_elements/cr_search_field/cr_search_field.js

-// Copyright 2015 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-var SearchField = Polymer({
-  is: 'cr-search-field',
-
-  behaviors: [CrSearchFieldBehavior],
-
-  properties: {
-    value_: String,
-  },
-
-  /** @return {!HTMLInputElement} */
-  getSearchInput: function() {
-    return this.$.searchInput;
-  },
-
-  /** @private */
-  clearSearch_: function() {
-    this.setValue('');
-    this.getSearchInput().focus();
-  },
-
-  /** @private */
-  toggleShowingSearch_: function() {
-    this.showingSearch = !this.showingSearch;
-  },
-});