Dependency of z3 was deleted?

[czheo]

1. It seems like an accident?
   654fb9a
2. Also, the repo of z3 has been moved to https://github.com/Z3Prover/z3
   • announcement: https://z3.codeplex.com/
   • outdated submodule config: https://github.com/palvaro/molly/blob/master/.gitmodules#L6

[JoshRosen]

Way back I submitted #2 to update the location of the Z3 submodule, so that could be used as an easy fix.