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/service.go

@@ -16,10 +16,6 @@ import (
 	"golang.org/x/sys/windows/svc/mgr"
 )
 
-func init() {
-	registerCollector("service", NewserviceCollector)
-}
-
 var (
 	serviceWhereClause = kingpin.Flag(
 		"collector.service.services-where",