Configure POSIX resource limits using ulimit

This amounts to removing the explicit handling since the resource limits
already work if provided by the system.

I believe this draws the correct boundary since I don't believe it is
appropriate for the builder-client to set its own resource limits.
Explain ulimit alternative
Merge pull request #2 from AlainODea-haskell/ImpliedResourceLimits

Configure POSIX resource limits using ulimit