Accessibility: deliverMatrixChoicesSurvey.jsp - Remove redundant onkeypress handler from "What is this" link

An onkeypress handler on the "What is this?" link causes a pop-up to appear when the user tabs around on the page.

The onkeypress handlers on the links and the form controls in the assessment delivery are redundant to the onclick handler and are causing problems for keyboard only users. For examples, please see the parent JIRA issue.

The onkeypress handler is not needed as Web Browsers will fire the onclick handler on buttons even if the button is activated by a keyboard interaction.

Suggested fix: Remove the redundant onkeypress handler from the "What's this?" link.