[ORC] NFC remove unimplemented query

Summary: CFGWalk Query is unimplemented for valid reasons. But the declaration got included in commit file.

Reviewers: lhames, dblaikie

Reviewed By: dblaikie

Subscribers: llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D66289

llvm-svn: 370085