[Z3] Bogus Z3Node>>#= leading to nightmare in Substitution

[shingarov]

While investigating the #fieldValue: mess in shingarov/Pharo-ArchC#36, I discovered strange lookup failures in #inEnvironment. It turns out we are relying on Z3 constants named x being equal (as in #=) to 'x'. This cannot possibly work, because Z3AST>>#hash is the Z3 hash.

[janvrany]

Ugh, this very wrong indeed.

I do not see other solution than to remove Z3Node >> #= and fix whatever it breaks (a lot, especially in ArchC, I suppose).