Remove dead parts from Torperf directory

The current Torperf directory contains at least two, maybe three files that can (and should) go away, because they blur the repository and confuse new users: README, run_test.py, and maybe plot_results.R. We should look if we still need something from these files and, if not, throw them away. While we're doing that, we could also update the LICENSE file.

I'm assigning this ticket to me. Will post a branch for others to review before merging.