Clean up some service profiler behavior in Conduit futures

Summary:
Correct two minor Conduit future issues:

• FutureAgent shows up in the trace log as "<mystery>". Since it isn't doing anything useful, solve the mystery and drop it from the log.
• Simply the ConduitFuture code for interacting with the service profiler now that a more structured integration is available.

Test Plan: Ran "arc branches --trace", saw conduit calls and no more "<mystery>" clutter.

Differential Revision: https://secure.phabricator.com/D21388