[#424] metrics: Drop embedded metrics

It was not obvious where metrics are used.

Signed-off-by: Dmitrii Stepanov <d.stepanov@yadro.com>

pkg/metrics/node.go

@@ -8,15 +8,12 @@ import (
 const namespace = "frostfs_node"
 
 type NodeMetrics struct {
-	objectServiceMetrics
-	engineMetrics
-	stateMetrics
-	replicatorMetrics
-
-	writeCacheMetrics *writeCacheMetrics
-	treeService       *treeServiceMetrics
-	epoch             prometheus.Gauge
-	gc                *gcMetrics
+	engine        *engineMetrics
+	state         *stateMetrics
+	replicator    *replicatorMetrics
+	objectService *objectServiceMetrics
+	treeService   *treeServiceMetrics
+	epoch         prometheus.Gauge
 }
 
 func NewNodeMetrics() *NodeMetrics {
@@ -37,19 +34,13 @@ func NewNodeMetrics() *NodeMetrics {
 		Help:      "Current epoch as seen by inner-ring node.",
 	})
 
-	writeCacheMetrics := newWriteCacheMetrics()
-
-	gc := newGCMetrics()
-
 	return &NodeMetrics{
-		objectServiceMetrics: objectService,
-		engineMetrics:        engine,
-		stateMetrics:         state,
-		replicatorMetrics:    replicator,
-		treeService:          treeService,
-		epoch:                epoch,
-		writeCacheMetrics:    writeCacheMetrics,
-		gc:                   gc,
+		objectService: objectService,
+		engine:        engine,
+		state:         state,
+		replicator:    replicator,
+		treeService:   treeService,
+		epoch:         epoch,
 	}
 }
 
@@ -58,18 +49,22 @@ func (m *NodeMetrics) SetEpoch(epoch uint64) {
 	m.epoch.Set(float64(epoch))
 }
 
-// WriteCache returns WriteCache metrics.
-func (m *NodeMetrics) WriteCache() WriteCacheMetrics {
-	if m == nil {
-		return nil
-	}
-	return m.writeCacheMetrics
-}
-
 func (m *NodeMetrics) TreeService() TreeMetricsRegister {
 	return m.treeService
 }
 
-func (m *NodeMetrics) GC() GCMetrics {
-	return m.gc
+func (m *NodeMetrics) Replicator() ReplicatorMetrics {
+	return m.replicator
+}
+
+func (m *NodeMetrics) ObjectService() ObjectServiceMetrics {
+	return m.objectService
+}
+
+func (m *NodeMetrics) Engine() EngineMetrics {
+	return m.engine
+}
+
+func (m *NodeMetrics) State() StateMetrics {
+	return m.state
 }