chore(s3/lifecycle): trim verbose comments

Cut multi-paragraph headers and what-the-code-does narration across the
Phase 3 rate-limit plumbing. Kept the small WHY notes (rate.Limiter
needs burst>=1, base ClusterContext is shared across parallel jobs,
contract sync between admin and worker constant pairs). Same code,
139 fewer lines of comment.

weed/admin/plugin/plugin.go

@@ -649,12 +649,6 @@ func (r *Plugin) executeJobWithExecutor(
 		return nil, err
 	}
 
-	// Apply per-job-type cluster-allocation decoration (e.g. s3_lifecycle
-	// divides cluster_deletes_per_second by min(workers, maxJobsPerDetection)
-	// and ships the share via ClusterContext.Metadata). No-op for job
-	// types without an allocator registered. MaxJobsPerDetection caps
-	// the divisor so a singleton job (maxJobs=1) gets the full budget on
-	// the single active worker, not 1/N of it.
 	clusterContext = r.decorateClusterContextForJob(clusterContext, job.JobType, adminConfigValues, int(adminRuntime.GetMaxJobsPerDetection()))
 
 	completedCh := make(chan *plugin_pb.JobCompleted, 1)