[chore] remove TODO from confmap code (open-telemetry#10278)

Remove a TODO comment on confmap/provider.go related to ChangeEvent.
This struct is used extensively in providers that rely on changes such
as:

https://github.com/signalfx/splunk-otel-collector/blob/main/internal/configsource/etcd2configsource/source.go#L84

confmap/provider.go

@@ -89,7 +89,6 @@ type Provider interface {
 type WatcherFunc func(*ChangeEvent)
 
 // ChangeEvent describes the particular change event that happened with the config.
-// TODO: see if this can be eliminated.
 type ChangeEvent struct {
 	// Error is nil if the config is changed and needs to be re-fetched.
 	// Any non-nil error indicates that there was a problem with watching the config changes.