[PING][PATCH v2] Remove check for NULL buffer passed to `ptsname_r'

[Zack Weinberg]

> `ptsname_r' is declared in stdlib.h to only accept a `nonnull'
> second argument and therefore GCC may choose to make optimizations
> based on the assumption that this argument is NULL. This means
> that potentially, GCC can optimize away the NULL check at some
> point in the future. Since this is a programming interface, we
> might as well remove the NULL check ourselves.
>
> This also warrants a change to the `ptsname_r' manual page that
> must be submitted to the corresponding mailing list.

Is this function documented in our manual (manual/*.texi)? If so,
please update that.

OK with that change.  I don't think we need a copyright assignment for
a change that deletes seven lines of code and adds none.

zw