Summary:
Just couple of small changes:
1. removed signal_test, since it doesn't seem useful and we don't even run it as part of `make check`
2. moved perf_context_test to TESTS instead of PROGRAMS
3. `make release` probably shouldn't compile benchmarks. We currently rely on `make release` building db_bench (via Jenkins), so I left db_bench there.

This is just a minor cleanup. We need to rethink our targets since they are a bit messy right now. We can do this during our tech debt week.

Test Plan: make release

Reviewers: anthony, rven, yhchiang, sdong, meyering

Reviewed By: meyering

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D36171