Modify deobfuscated IL in place

[toshipiazza]

Blocking on Vector35/binaryninja-api#1606

Right now, we undo control flow flattening by patching the binary and saving it to disk. Now that binja has a decompiler, it's worth updating the IL instead, keeping everything platform-independent.

Since we're completely reconstructing the function, I see two solutions here:

1. incrementally update control flow, re-placing phi nodes as we go (or)
2. completely re-build the IL for the function w/ correct control flow fixups

But it all depends on how the feature works in binja when it's ready

[toshipiazza]

This also makes it easier to deobfuscate OLLVM's opaque predicates, which we currently don't bother doing.