message: removed all unnecessary functions
diff: import browser from "webextension-polyfill";
  let panelId = undefined;
  -const windowOpenSideex = {};
  -
  -function onCreated(windowInfo) {
  - console.log(`Create editor successfully: id = ${windowInfo.id}`);
  - panelId = windowInfo.id;
  -}
  -
  -function onError(error) {
  - console.log(`Error: ${error}`);
  -}
  -
  -function checkOpenOneSideex(contentWindowInfo) {
  - console.log("contentWindowInfo1-2: ", contentWindowInfo);
  - if (windowOpenSideex[contentWindowInfo.id] !== undefined && windowOpenSideex[contentWindowInfo.id] == true) {
  - console.log("Sideex has been opened.");
  - console.log("windowOpenSideex: ", windowOpenSideex);
  - return Promise.reject("Sideex has been opened.");
  - }
  - windowOpenSideex[contentWindowInfo.id] = true;
  - console.log("Open one sideex.");
  - console.log("contentWindowInfo2: ", contentWindowInfo);
  - return contentWindowInfo;
  -}
  -
  -function openSideexWindow(contentWindowInfo) {
  - let sideexWindowInfo = browser.windows.create({
  - url: browser.extension.getURL("assets/panel.html"),
  - type: "popup",
  - height: 730,
  - width: 750
  - });
  - console.log("contentWindowInfo3: ", contentWindowInfo);
  - console.log("sideexWindowInfo: ", sideexWindowInfo);
  - return sideexWindowInfo;
  -}
  function openPage() {
  -
  const getContentWindowInfo = browser.windows.getLastFocused();
  const getSideexWindowInfo = browser.windows.create({
  url: browser.extension.getURL("assets/panel.html"),
  