Save keyfreqs can fail when visiting remote host

At https://github.com/dacap/keyfreq/blob/main/keyfreq.el#L465 the (list-system-processes) function is called, but when default-directory is on a remote host, this attempts to lists the processes on that host. This can lead to latency and even get stuck when there's problems with tramp.

Maybe it's an idea to do something like (let ((default-directory "")) (list-system-processes)) to get the local processes?