Hygiene: Tidy up QUnit references

Since Ieea378c9 all QUnit tests are run in Node.js and not in the
browser. Tidy up references to QUnit inside of the codebase and tooling.

Changes:
* Don't exclude src/processLinks.js in Istanbul code coverage reports.
* Don't test for window.QUnit in createSchema. We no longer run the risk
  of sending beacons while running the QUnit test suite as it's no
  longer run in the browser.

Bug: T160406
Change-Id: Ifb6adb84b8019dd69231b50af00bf978b708fc60

.istanbul.yml

@@ -3,6 +3,5 @@ instrumentation:
   excludes: [
     "resources/dist/*", # Compiled assets
     "*.js", # Gruntfile.js and webpack.config.js
-    "src/processLinks.js", # Covered by browser QUnit integration test
     "src/index.js", # Application entry point
   ]

src/schema.js

@@ -14,8 +14,7 @@ module.exports = function ( config, window ) {
 
 	if (
 		!window.navigator ||
-		!$.isFunction( window.navigator.sendBeacon ) ||
-		window.QUnit
+		!$.isFunction( window.navigator.sendBeacon )
 	) {
 		samplingRate = 0;
 	}

tests/node-qunit/schema.test.js

@@ -55,13 +55,3 @@ QUnit.test( 'it should use a 0 sampling rate when sendBeacon isn\'t supported',
 
 	assert.deepEqual( mw.eventLog.Schema.getCall( 1 ).args, expectedArgs );
 } );
-
-QUnit.test( 'it should use a 0 sampling rate in a unit testing environment', function ( assert ) {
-	assert.expect( 1 );
-
-	this.window.QUnit = {};
-
-	createSchema( this.config, this.window );
-
-	assert.ok( mw.eventLog.Schema.calledWith( 'Popups', 0 ) );
-} );