llvm-uselistorder: Fix memory leak from r214125

Turns out `parseBitcodeFile()` does *not* take ownership of the buffer.
This was already clear in the header docs, but I obviously didn't read
them (having noticed that it gets stored in a `unique_ptr<>`).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@214313 91177308-0d34-0410-b5e6-96231b3b80d8