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/adfs.go

@@ -8,10 +8,6 @@ import (
 	"math"
 )
 
-func init() {
-	registerCollector("adfs", newADFSCollector, "AD FS")
-}
-
 type adfsCollector struct {
 	adLoginConnectionFailures                          *prometheus.Desc
 	certificateAuthentications                         *prometheus.Desc