Fixup: Simplify type annotation for ident

Also, with a type annotation for ident, showName becomes unnecessary.
The type annotation on langName is not needed for ambiguity, just for
documentation.
Fixup: PTSName ↦ LanguageName

In
https://github.com/Blaisorblade/pts/commit/3f5d125ba5e566e10000f08aa7e28f62917ea87b#commitcomment-7362848
Tillmann wrote:

> Can we call this LanguageName, as part of a slow move towards using
"language" more and "PTS" less. Reason: In the future, I consider
non-PTS language options like "records available" or "type inference
enabled".