forall statement with no bound variables is deprecated in `ModInternals`

[seebees]

Update ModInternals to use assert by

Example:

src/NonlinearArithmetic/Internals/ModInternals.dfy(94,4): Warning: a forall statement with no bound variables is deprecated; use an 'assert by' statement instead

[MikaelMayer]

I have tried a lot but there is something different with non-linear arithmetic that I don't know why but can't prove at all.