remove perf/ folder

[juliasloan25]

The performance of ClimaCoupler is as good as we need it to be for the foreseeable future. In addition, the runs produced by drivers/scripts in the perf/ folder are largely not looked at currently. Because of this, we can remove the perf/ folder altogether. As we do this, we should note the commit that removes it in our README, so that we can easily bring it back in the future if it becomes helpful again.