Remove Data.LLVM.CFG?

[langston-barrett]

It appears to only be used within this package to print GraphViz code via the CLI and in the defunct llvm-verifier. Given that GraphViz visualization can be accomplished via opt, I'm not convinced of the utility of maintaining our own version. We could likely remove a dependency or two if we do remove this.

[RyanGlScott]

If we can achieve everything that llvm-disasm does via opt, then I'm definitely open to the idea of removing this code.