docs: remove obsolete info in getting started
docs: remove obsolete info in getting started

Go automatically configures the number of used threads appropriately
and tweaking it is no longer relevant for a basic setup of Prometheus.
The baseline consumption tied to the storage layer no longer applies.

kangwoo/prometheus,alileza/prometheus,Conorbro/prometheus,Gouthamve/prometheus,amorken/prometheus,amorken/prometheus,Gouthamve/prometheus,AlekSi/prometheus,AlekSi/prometheus,keegancsmith/prometheus,Conorbro/prometheus,GoogleCloudPlatform/prometheus,brancz/prometheus,Gouthamve/prometheus,Stackdriver/stackdriver-prometheus,Conorbro/prometheus,brancz/prometheus,amorken/prometheus,brancz/prometheus,keegancsmith/prometheus,alileza/prometheus,kangwoo/prometheus,keegancsmith/prometheus,GoogleCloudPlatform/prometheus,Stackdriver/stackdriver-prometheus,prometheus/prometheus,GoogleCloudPlatform/prometheus,kangwoo/prometheus,Stackdriver/stackdriver-prometheus,Conorbro/prometheus,keegancsmith/prometheus,prometheus/prometheus,alileza/prometheus,prometheus/prometheus,keegancsmith/prometheus,prometheus/prometheus,alileza/prometheus,AlekSi/prometheus,amorken/prometheus,Gouthamve/prometheus,brancz/prometheus,AlekSi/prometheus,prometheus/prometheus,Stackdriver/stackdriver-prometheus,GoogleCloudPlatform/prometheus,alileza/prometheus,GoogleCloudPlatform/prometheus,kangwoo/prometheus