check-code: drop the camelcase checks
Fro about 2 years we have been using CamelCase is class names. That rules gets
in the way of assigning class or exception in compatibility layers.
I think it is safe to drop it now that we started using CamelCase for some case.
My motivation for this is the need to assign `FileNotFoundError` in `pycompat`.
Differential Revision: https://phab.mercurial-scm.org/D11309
#require docutils gettext
$ $TESTDIR/check-gendoc ru
checking for parse errors