feat: Remove init functions from collectors

Behaviour of init functions has been centralised in `collector/init.go`,
and can be called during exporter startup. This allows the exporter to
control the timing of collector initialisation, rather than relying on
the import & `init()` method.

This should reduce unexpected behaviour arising from the use of
`init()`, such as #551.

Signed-off-by: Ben Reedy <breed808@breed808.com>

collector/cpu_info.go

@@ -13,10 +13,6 @@ import (
 	"github.com/yusufpapurcu/wmi"
 )
 
-func init() {
-	registerCollector("cpu_info", newCpuInfoCollector)
-}
-
 // If you are adding additional labels to the metric, make sure that they get added in here as well. See below for explanation.
 const (
 	win32ProcessorQuery = "SELECT Architecture, DeviceId, Description, Family, L2CacheSize, L3CacheSize, Name FROM Win32_Processor"