Remove the bus.EventAvailableReleases implementation (#496)

to let the kairos-agent handle upgrades from now on. It used to be that
provider-kairos returned releases from the provider-kairos repository
but it's no longer the case. Everything is release in the
kairos-io/kairos repository and the new versioneer library of the
kairos-sdk (which is used in the kairos-agent) is capabable of handling
both "standard" and "core" images.

Part of: kairos-io/kairos#1999

Signed-off-by: Dimitris Karakasilis <dimitris@karakasilis.me>

internal/provider/start.go

@@ -27,7 +27,5 @@ func Start() error {
 
 	factory.Add(bus.EventInteractiveInstall, InteractiveInstall)
 
-	factory.Add(bus.EventAvailableReleases, ListVersions)
-
 	return factory.Run(pluggable.EventType(os.Args[1]), os.Stdin, os.Stdout)
 }