Replace sysinfo crate

[andresilva]

The sysinfo crate has caused us some trouble due to the amount of file descriptors it keeps open (#6805). We should look into replacing this crate with something simpler. We seem to only be using it for fetching the average cpu usage and memory (currently working on multiple OS's). All of the process specific info (e.g. number of threads, number of file handles) we are getting directly from procfs and as such we only have Linux support currently.

[andresilva]

#6805 removed sysinfo on Linux (data is fetched through procfs), it is still used on macos and windows.