test: refactor large event emitter tests

This commit splits several large event emitter tests into smaller
block scoped tests. This keeps the tests more isolated. This
commit also replaces var with const, assert.equal() with
assert.stictEqual(), and other small enhancements.

PR-URL: #6446
Reviewed-By: Santiago Gimeno <santiago.gimeno@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

test/parallel/test-event-emitter-remove-listeners.js

@@ -1,13 +1,13 @@
 'use strict';
 const common = require('../common');
 const assert = require('assert');
-const EventEmitter = require('events');
+const events = require('events');
 
 function listener1() {}
 function listener2() {}
 
 {
-  const ee = new EventEmitter();
+  const ee = new events.EventEmitter();
   ee.on('hello', listener1);
   ee.on('removeListener', common.mustCall((name, cb) => {
     assert.strictEqual(name, 'hello');
@@ -18,15 +18,15 @@ function listener2() {}
 }
 
 {
-  const ee = new EventEmitter();
+  const ee = new events.EventEmitter();
   ee.on('hello', listener1);
   ee.on('removeListener', common.fail);
   ee.removeListener('hello', listener2);
   assert.deepStrictEqual([listener1], ee.listeners('hello'));
 }
 
 {
-  const ee = new EventEmitter();
+  const ee = new events.EventEmitter();
   ee.on('hello', listener1);
   ee.on('hello', listener2);
   ee.once('removeListener', common.mustCall((name, cb) => {
@@ -46,7 +46,7 @@ function listener2() {}
 }
 
 {
-  const ee = new EventEmitter();
+  const ee = new events.EventEmitter();
 
   function remove1() {
     common.fail('remove1 should not have been called');
@@ -67,7 +67,7 @@ function listener2() {}
 }
 
 {
-  const ee = new EventEmitter();
+  const ee = new events.EventEmitter();
   ee.on('hello', listener1);
   ee.on('hello', listener2);
   ee.once('removeListener', common.mustCall((name, cb) => {
@@ -87,7 +87,7 @@ function listener2() {}
 }
 
 {
-  const ee = new EventEmitter();
+  const ee = new events.EventEmitter();
   const listener3 = common.mustCall(() => {
     ee.removeListener('hello', listener4);
   }, 2);
@@ -106,7 +106,7 @@ function listener2() {}
 }
 
 {
-  const ee = new EventEmitter();
+  const ee = new events.EventEmitter();
 
   ee.once('hello', listener1);
   ee.on('removeListener', common.mustCall((eventName, listener) => {