removes redundant #qunit-scratch (use standard #qunit-fixture instead)

In addition to the standard #qunit-fixture there was also a custom #qunit-scratch element used in JS test suite (it was used only by a single test: click_track_test.js). There is no need for such a custom element (especially considering that the default #qunit-fixture is superior as it is auto clean up by QUnit runtime - in case of #qunit-scratch it has to be explicitely cleabed in teardown).

This pull request removes this redundant element from the suite and refactors click_track_test.js to use standard #qunit-fixture instead.