Drop the udis86 wrapper from llvm::sys

This optional dependency on the udis86 library was added some time back to aid
JIT development, but doesn't make much sense to link into LLVM binaries these
days.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@213300 91177308-0d34-0410-b5e6-96231b3b80d8