Remove SystemJS usage, in development mode, from the worker

Now that https://bugzilla.mozilla.org/show_bug.cgi?id=1247687 has landed in Firefox, we're able to use worker-modules during development :-)

This removes the final piece of SystemJS usage from the PDF.js library, thus allowing a fair bit of clean-up, and we now use *only* native `import`/`export` statements everywhere in development mode.

src/core/.eslintrc

@@ -1,13 +0,0 @@
-{
-  "parserOptions": {
-    "ecmaVersion": 2017,
-  },
-
-  "extends": [
-    "../../.eslintrc"
-  ],
-
-  "env": {
-    "es2017": true,
-  },
-}

src/core/unicode.js

@@ -12,7 +12,6 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-/* no-babel-preset */
 
 import { getLookupTableFactory } from "./core_utils.js";
 

src/display/api.js

@@ -2130,12 +2130,9 @@ class PDFWorker {
           );
         }
 
-        // Some versions of FF can't create a worker on localhost, see:
-        // https://bugzilla.mozilla.org/show_bug.cgi?id=683280
         const worker =
           typeof PDFJSDev === "undefined" &&
-          !workerSrc.endsWith("/build/pdf.worker.js") &&
-          !workerSrc.endsWith("/src/worker_loader.js")
+          !workerSrc.endsWith("/build/pdf.worker.js")
             ? new Worker(workerSrc, { type: "module" })
             : new Worker(workerSrc);
         const messageHandler = new MessageHandler("main", "worker", worker);

src/shared/.eslintrc

@@ -1,13 +0,0 @@
-{
-  "parserOptions": {
-    "ecmaVersion": 2017,
-  },
-
-  "extends": [
-    "../../.eslintrc"
-  ],
-
-  "env": {
-    "es2017": true,
-  },
-}

src/worker_loader.js

@@ -1,32 +0,0 @@
-/* Copyright 2012 Mozilla Foundation
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-"use strict";
-
-// Patch importScripts to work around a bug in WebKit and Chrome 48-.
-// See https://crbug.com/572225 and https://webkit.org/b/153317.
-self.importScripts = (function (importScripts) {
-  return function () {
-    setTimeout(function () {}, 0);
-    return importScripts.apply(this, arguments);
-  };
-})(importScripts);
-
-importScripts("../node_modules/systemjs/dist/system.js");
-importScripts("../systemjs.config.js");
-
-SystemJS.import("pdfjs/core/worker.js").then(function () {
-  // Worker is loaded at this point.
-});