[css-syntax] CDO Token railroad diagram

[Crissov]

The legacy CDO token looks like an opening HTML comment: <!--. In its railroad diagram however, the character sequence is <<!---->!--. This seems like an editorial mistake or possibly an attempt to circumvent Bikeshed actually starting a comment there by throwing in an empty comment <!----> instead of escaping the angle bracket > or something similar.

[tabatkins]

Indeed. I'm not even sure exactly what I was doing there, but it must have been working around a Bikeshed parsing bug which no longer exists. Fixed.