It should have been removed by q2 uninstall. I do see that extension is uninstalled now, not sure why it wasn't removed when you uninstalled it. Possibly because of some of the initial other attempts.
None the less, it is gone now.
For reference, the script is placed in a UiConfigPropertyDataElement/UiConfigPropertyData entry. The Element name is "Q2_SECURITY_SECURITY_THIRD_PARTY_HTML_BLOCK" ... you can lookup the PropertyID of that in UiConfigPropertyDataElement table and then take that PropetyID and go to the UiConfigPropertyData table and change/remove the value.