Don't assert that comparator arguments are non-equal.

Don't assert that comparator arguments are non-equal.

Comparator is used in 'std::sort'.
All items in closure have unnique TNFA states, therefore we assumed
that the compared items must always be different. However, 'std::sort'
does not have this requirement and some implementations of it compare
the element with itself.

The removed assert caused crashes with old version of GCC (4.2).

Thanks to Sergei Trofimovich for debugging the issue.