The _total suffix is by convention for counters,
don't use it on a gauge. Clarify help string.
Tweak metric name so it'll sort with related metrics,
and be a little more understandable.
Remove open file descriptor metric, as Prometheus client_golang
provides that out of the box as process_open_fds which is also
more up to date. Both only support Linux, so there's no loss of
platform support.
Fixes#5229
ea1d0f3e0d