swarm: fix megacheck warnings

swarm/storage/dpa.go

@@ -59,7 +59,6 @@ type DPA struct {
 
 	lock    sync.Mutex
 	running bool
-	wg      *sync.WaitGroup
 	quitC   chan bool
 }
 
@@ -239,6 +238,4 @@ func (self *dpaChunkStore) Put(entry *Chunk) {
 }
 
 // Close chunk store
-func (self *dpaChunkStore) Close() {
-	return
-}
+func (self *dpaChunkStore) Close() {}