No analog of assert forall by for forall_arith; deprecate forall_arith?

[jaylorch]

It would be nice if one could do assert forall_arith |x| <some arithmetic expression> by { <proof> } to establish forall_arith |x| <some arithmetic expression>, analogously to how one can do assert forall |x| <some normal expression> by { <proof> }.

[Chris-Hawblitzel]

Maybe the thing to do is to combine forall and forall_arith into a uniform forall, and just restrict the uses of the quantified variables to avoid boxing/triggering issues.

[utaal]

Addressed by #625.

Shall we deprecate forall_arith once #625 is merged?

[utaal]

forall_arith has been removed in eb54500.