Outdated references in test harness html files

[k-jensen]

Subject of the issue/enhancement/features

When using the test html files to locally test the xapi functionality, the Adapt course is not being displayed properly. There are also outdated references to

<button id="accessibility-toggle" class="base button a11y-ignore-focus" role="button" ></button>
<span id="accessibility-instructions" class="aria-label" role="region" tabindex="0"></span>

Your environment

• Framework version 3+

Steps to reproduce

• Build an adapt course with the xapi extension enabled.
• serve the course and navigate to one of the test harness html files (xapi_test_harness.html or xapi_adl_test_harness.html)

Expected behaviour

The adapt course should preview as normal, with correct styling.

Actual behaviour

The adapt course appears without styling. Caused by https://github.com/adaptlearning/adapt_framework/pull/1932 ?