Do not increase nice-ness of benchmarked process
Do not increase nice-ness of benchmarked process

This was never documented, can influence the performance of the
benchmarked process, and can be easily done by the user themselves if
desired, so there is no reason for BenchExec to do it.

ultimate-pa/benchexec,ultimate-pa/benchexec,ultimate-pa/benchexec,dbeyer/benchexec,sosy-lab/benchexec,ultimate-pa/benchexec,ultimate-pa/benchexec,dbeyer/benchexec,sosy-lab/benchexec,sosy-lab/benchexec,dbeyer/benchexec,dbeyer/benchexec,ultimate-pa/benchexec,sosy-lab/benchexec,sosy-lab/benchexec,sosy-lab/benchexec