/classes endpoint does not work in a browser

[tloubrieu-jpl]

🐛 Describe the bug

I believe this can be reproduced with curl request:
curl http://localhost:8081/classes -H 'Accept:text/html'

[alexdunnjpl]

@tloubrieu-jpl I replicated this (having neglected to update main from its few-week-old version) and wrote a fix, but with an updated version of main I'm no longer able to replicate it. I thought it might have been incidentally resolved in 87814ae or 1ce1306, but it's non-reproducible even as of revision e2162a1 (and going much further back is turning out to be more of a pain than it's worth due to environment minutiae).

Suggest closing as it's no longer reproducible, but it's relevant that ClassesSerializer is not included in the converters and it's still the case that the log message is in the wrong place (it checks size before anything's actually added, so always logs zero converters) so that fix (ae6ce91) should still make it in.

Should the ClassesSerializer be added to the converters, or deleted from the codebase, given that it appears unnecessary?

[tloubrieu-jpl]

Right I am not reproducing it either, this has been field without knowing as a consequence of ticket #248