Replace jsReady.js and moduleReady.js with waitForNetworkIdle call

I'm hopeful that we can replace jsReady.js and moduleReady.js which wait for
particular js modules to load with a simple call to `page.waitForNetworkIdle`
instead. This should also be more future-proof. If not, we can revert this.

Author: Nicholas Ray

src/engine-scripts/puppet/echo.js

@@ -1,5 +1,3 @@
-const moduleReady = require( './moduleReady' );
-
 /**
  * Setup Echo notifications
  *
@@ -15,15 +13,12 @@ module.exports = async ( page, hashtags ) => {
 
 	// Open the drawer for tests that require interaction
 	if ( hashtags.includes( '#echo-drawer' ) ) {
-		await moduleReady( page, 'ext.echo.init' );
 		await page.evaluate( async () => {
 			const btn = document.querySelector( '#pt-notifications-alert a' );
 			btn.click();
 		} );
-		await moduleReady(
-			page,
-			hashtags.includes( '#mobile' ) ? 'ext.echo.mobile' : 'ext.echo.ui.desktop'
-		);
+		// Wait for JS to load.
+		await page.waitForNetworkIdle();
 
 		// Wait for the OOUI pending element to disappear.
 		await page.waitForSelector( '.oo-ui-pendingElement-pending', {

src/engine-scripts/puppet/jsReady.js

@@ -12,8 +12,8 @@ module.exports = async ( page, scenario ) => {
 	const label = scenario.label;
 	const hashtags = label.match( /(#[^ ,)]*)/g ) || [];
 
-	// Make sure the main skin JavaScript module has loaded.
-	await require( './jsReady' )( page, hashtags );
+	// Wait for async js to finish loading.
+	await page.waitForNetworkIdle();
 
 	if ( hashtags.includes( '#scroll' ) ) {
 		await require( './scroll.js' )( page );

src/engine-scripts/puppet/moduleReady.js

@@ -1,4 +1,3 @@
-const moduleReady = require( './moduleReady' );
 const fastForwardAnimations = require( './fastForwardAnimations' );
 
 /**
@@ -49,8 +48,9 @@ module.exports = async ( page, hashtags ) => {
 	} else {
 		// Make sure Codex kicked in.
 		await page.waitForSelector( '.cdx-typeahead-search' );
-		// Wait for Vue to load.
-		await moduleReady( page, 'vue' );
+
+		// Wait for JS to load.
+		await page.waitForNetworkIdle();
 		// focus and type into the newly added input
 		await page.focus( selectorSearchInput );
 		await page.keyboard.type( 't' );