[Tooling] Don't deduplicate tool results in the All-TUs executor.

Summary:
As result deduplication or reduction is not supported in the framework,
we should leave the deplication to tools (if needed) until the framework supports it.

Reviewers: bkramer

Subscribers: klimek, cfe-commits

Differential Revision: https://reviews.llvm.org/D42111

llvm-svn: 322691