CLC-4212 - Updated to replace entire error message, rather than just modifying example input

https://jira.ets.berkeley.edu/jira/browse/CLC-4212

Canvas BETA provides new error message content not seen in production - "If your format is correct, contact your Canvas Admin to ensure the user has a Canvas account". Updated Javascript to replace the entire error message, thus ensuring this does not show up in production in the weeks to come.

QA in #2908