feat(s3/lifecycle): drop Worker Count knob from admin config form

The "Worker Count" admin field controlled in-process pipeline goroutines
across the 16-shard space — per-worker tuning, not a cluster-wide scope
concern. Operators looking at the form alongside Cluster Delete Rate
reasonably misread it as the number of workers in the cluster.

Drop the form field and DefaultValues entry. cfg.Workers is now hardcoded
to shardPipelineGoroutines (=1) inside ParseConfig; the rest of the
plumbing through dailyrun.Config.Workers stays so a future need can
re-introduce it as a worker-local knob (or just bump the constant).

handler_test.go pins that "workers" must NOT appear in the form so the
removal doesn't silently regress.

weed/worker/tasks/s3_lifecycle/handler.go

@@ -74,17 +74,8 @@ func (h *Handler) Descriptor() *plugin_pb.JobTypeDescriptor {
 				{
 					SectionId:   "scope",
 					Title:       "Scope",
-					Description: "How many pipeline goroutines split the 16-shard space.",
+					Description: "Cluster-wide algorithm choice and delete-throughput cap.",
 					Fields: []*plugin_pb.ConfigField{
-						{
-							Name:        "workers",
-							Label:       "Worker Count",
-							Description: "Number of pipeline goroutines per executing worker. Each owns a contiguous slice of [0, 16) shards. Default 1 = one goroutine handles all 16 shards.",
-							FieldType:   plugin_pb.ConfigFieldType_CONFIG_FIELD_TYPE_INT64,
-							Widget:      plugin_pb.ConfigWidget_CONFIG_WIDGET_NUMBER,
-							MinValue:    &plugin_pb.ConfigValue{Kind: &plugin_pb.ConfigValue_Int64Value{Int64Value: 1}},
-							MaxValue:    &plugin_pb.ConfigValue{Kind: &plugin_pb.ConfigValue_Int64Value{Int64Value: 16}},
-						},
 						{
 							Name:        "algorithm",
 							Label:       "Algorithm",
@@ -116,7 +107,6 @@ func (h *Handler) Descriptor() *plugin_pb.JobTypeDescriptor {
 				},
 			},
 			DefaultValues: map[string]*plugin_pb.ConfigValue{
-				"workers":                       {Kind: &plugin_pb.ConfigValue_Int64Value{Int64Value: defaultWorkers}},
 				"algorithm":                     {Kind: &plugin_pb.ConfigValue_StringValue{StringValue: defaultAlgorithm}},
 				ClusterDeletesPerSecondAdminKey: {Kind: &plugin_pb.ConfigValue_Int64Value{Int64Value: 0}},
 				ClusterDeletesBurstAdminKey:     {Kind: &plugin_pb.ConfigValue_Int64Value{Int64Value: 0}},