Continuing experimental printing of the signature of open evars in
Check (see cfff8f8a327) [printing only visible evars, not the ones
corresponding to unrelated open goals + fixing bug on wrong sigma and
on evar_info normalization].
Dead code.
More precise test for #3459.
Adapting output tests to the removal of the new token warning and to
the printing of the context of open evars in Check.