Several suggestions how to deal with this without moderator's intervention are listed here: Workaround for broken comments. (I should probably add that while moderators can edit the comment, the only think you can do - even with using the above workarounds - is to delete it. So it the comment contains some relevant reputation, you might try to note it somewhere, so that it is not lost.)
To be more specific, the approach using scaling math size is suggested in Willie Wong's answer. And Asaf Karagila's answer suggests using developer tools. In his comments here Asaf also explains how to delete the sidebar.
One additional suggestion from me: Try to change Math Renderer in MathJax settings. (A screenshot showing how to do this can be found, for example, here. It is probably easier if you right click on MathJax code that works rather than on the problematic part.) Even if some renderers still have this problem, choosing Plain Source as Math Renderer should help you to be able to delete the comment. (As pointed out in Davide Cervone's comment.)
This is how your comment looks for me with SVG:
This is how it looks with HTML-CSS:
Since in the first case the comment is not stretched wide, I guess to the author of the comment also the delete-comment button is shown.