Alerting: Update scheduler to get updates only from database (#64635)

* stop using the scheduler's Update and Delete methods all communication must be via the database
* update scheduler's registry to calculate diff before re-setting the cache
* update fetcher to return the diff generated by registry
* update processTick to update rule eval routine if the rule was updated and it is not going to be evaluated at this tick.
* remove references to the scheduler from api package
* remove unused methods in the scheduler

pkg/services/ngalert/api/api.go

@@ -18,7 +18,6 @@ import (
 	"github.com/grafana/grafana/pkg/services/ngalert/models"
 	"github.com/grafana/grafana/pkg/services/ngalert/notifier"
 	"github.com/grafana/grafana/pkg/services/ngalert/provisioning"
-	"github.com/grafana/grafana/pkg/services/ngalert/schedule"
 	"github.com/grafana/grafana/pkg/services/ngalert/sender"
 	"github.com/grafana/grafana/pkg/services/ngalert/state"
 	"github.com/grafana/grafana/pkg/services/ngalert/store"
@@ -66,7 +65,6 @@ type API struct {
 	DatasourceService    datasources.DataSourceService
 	RouteRegister        routing.RouteRegister
 	QuotaService         quota.Service
-	Schedule             schedule.ScheduleService
 	TransactionManager   provisioning.TransactionManager
 	ProvenanceStore      provisioning.ProvisioningStore
 	RuleStore            RuleStore
@@ -116,7 +114,6 @@ func (api *API) RegisterAPIEndpoints(m *metrics.API) {
 		&RulerSrv{
 			conditionValidator: api.EvaluatorFactory,
 			QuotaService:       api.QuotaService,
-			scheduleService:    api.Schedule,
 			store:              api.RuleStore,
 			provenanceStore:    api.ProvenanceStore,
 			xactManager:        api.TransactionManager,