Remove unessential and dead code paths from dev-llgs-local-launch branch.

This removes:
* fork-sync-exec launching.
* Shawn's 5-second timeout code that was meant to address what ended up being a UnixSignals issue.
  I'm not comfortable leaving that in since it ultimately wasn't related to the issue we put it in for.

Implements https://github.com/tfiala/lldb/issues/60.