Fix spec on ruby != (1.9.(2|3)).

On 1.9.2 and 1.9.3, Proc#== briefly attempted
to return true if the procs had the same body.
I was surprised to see this behavior earlier today
when I wrote this spec, and left the spec in place
thinking it must have always been that way but I
just never knew it.

As it turns out, that was only the case on 1.9.2 and 1.9.3
but it was half baked and never worked properly, and
got removed in 2.0:

https://bugs.ruby-lang.org/issues/4559