Prometheus: Remove flaky process collection NIF.

quote:

[7:19:12 pm] <href> remove the exporter process stuff, that's all-- the nif sucks
[7:19:23 pm] <href> all other metrics besides "beam process" will still work
[7:20:06 pm] <href> i was doing this already when dev because the nif sucks on freebsd. if there was a way to tell it was optional we'd keep it (some of the info is kinda useful)
[7:20:13 pm] <href> but it's not worth the pain of this nif