Remove VPULitElement/VPULitElementJQuery

We should try to avoid changing the DOM directly and these helpers go against that.
They both just add two lines of code which we can just copy around if needed.

packages/common/vpu-lit-element-jquery.js

-import VPULitElement from "./vpu-lit-element";
-import $ from "jquery";
-
-export default class VPULitElementJQuery extends VPULitElement {
-    $(selector) {
-        return $(this._(selector));
-    }
-}

packages/common/vpu-lit-element.js

-import {LitElement} from "lit-element";
-
-export default class VPULitElement extends LitElement {
-    _(selector) {
-        return this.shadowRoot === null ? this.querySelector(selector) : this.shadowRoot.querySelector(selector);
-    }
-}