Remove cumulative time limits and cpu time limits (#4711)

Remove cumulative time limits and cpu time limits (#4711)

This PR removes two things from the resource manager:

cumulative time limits
cpu time limits
Cumulative time limiting has been moved to the binary and is (as before) accessible via --tlimit. As per discussion among the devs, we no longer support time limits based on CPU time and thus everything related to that is removed as well.
Note that this includes the option --cpu-time, removes an argument from SmtEngine::setTimeLimit() and the method SmtEngine::getTimeRemaining() .