Collapse imports for file into one statement

This is a warning in the internal build system, and it does make the code a bit easier to read this way.

no-op change

lib/mixins/element-mixin.js

@@ -9,14 +9,13 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
 */
 import '../utils/boot.js';
 
-import { rootPath as rootPath$0 } from '../utils/settings.js';
+import { rootPath as rootPath$0, strictTemplatePolicy, allowTemplateFromDomModule } from '../utils/settings.js';
 import { dedupingMixin } from '../utils/mixin.js';
 import { stylesFromTemplate, stylesFromModuleImports } from '../utils/style-gather.js';
 import { pathFromUrl, resolveCss, resolveUrl as resolveUrl$0 } from '../utils/resolve-url.js';
 import { DomModule } from '../elements/dom-module.js';
 import { PropertyEffects } from './property-effects.js';
 import { PropertiesMixin } from './properties-mixin.js';
-import { strictTemplatePolicy, allowTemplateFromDomModule } from '../utils/settings.js';
 
 /**
  * Element class mixin that provides the core API for Polymer's meta-programming
@@ -273,7 +272,7 @@ export const ElementMixin = dedupingMixin(base => {
 
   /**
    * Look up template from dom-module for element
-   * 
+   *
    * @param {!string} is Element name to look up
    * @return {!HTMLTemplateElement} Template found in dom module, or
    *   undefined if not found
@@ -410,14 +409,14 @@ export const ElementMixin = dedupingMixin(base => {
       // - constructor._template: memoized version of constructor.template
       // - prototype._template: working template for the element, which will be
       //     parsed and modified in place. It is a cloned version of
-      //     constructor.template, saved in _finalizeClass(). Note that before 
+      //     constructor.template, saved in _finalizeClass(). Note that before
       //     this getter is called, for legacy elements this could be from a
       //     _template field on the info object passed to Polymer(), a behavior,
       //     or set in registered(); once the static getter runs, a clone of it
-      //     will overwrite it on the prototype as the working template. 
+      //     will overwrite it on the prototype as the working template.
       if (!this.hasOwnProperty(JSCompiler_renameProperty('_template', this))) {
         this._template =
-          // If user has put template on prototype (e.g. in legacy via registered 
+          // If user has put template on prototype (e.g. in legacy via registered
           // callback or info object), prefer that first
           this.prototype.hasOwnProperty(JSCompiler_renameProperty('_template', this.prototype)) ?
           this.prototype._template :