Enable ESLint rules that no longer need to be disabled on a directory/file-basis

Given that browsers/environments without native support for both arrow functions and object shorthand properties are no longer supported in PDF.js, please refer to the compatibility information below, we can now enable a fair number of ESLint rules and also simplify/remove some `.eslintrc` files.

With the exception of the `no-alert` cases, all code changes were made automatically by using `gulp lint --fix`.

 - https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/Arrow_functions#browser_compatibility
 - https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Object_initializer#browser_compatibility

examples/acroforms/acroforms.js

@@ -37,11 +37,11 @@ loadingTask.promise.then(function (doc) {
         return doc.getPage(pageNum).then(function (pdfPage) {
           // Create the page view.
           var pdfPageView = new pdfjsViewer.PDFPageView({
-            container: container,
+            container,
             id: pageNum,
             scale: DEFAULT_SCALE,
             defaultViewport: pdfPage.getViewport({ scale: DEFAULT_SCALE }),
-            eventBus: eventBus,
+            eventBus,
             annotationLayerFactory: new pdfjsViewer.DefaultAnnotationLayerFactory(),
             renderInteractiveForms: true,
           });