libnetwork/internal/kvstore/boltdb: fix linting issues

    libnetwork/internal/kvstore/boltdb/boltdb.go:452:28: unnecessary conversion (unconvert)
                _ = bucket.Delete([]byte(key))
                                        ^
    libnetwork/internal/kvstore/boltdb/boltdb.go:425:2: S1023: redundant `return` statement (gosimple)
        return
        ^

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

libnetwork/internal/kvstore/boltdb/boltdb.go

@@ -422,7 +422,6 @@ func (b *BoltDB) Close() {
 	} else {
 		b.client.Close()
 	}
-	return
 }
 
 // DeleteTree deletes a range of keys with a given prefix
@@ -449,7 +448,7 @@ func (b *BoltDB) DeleteTree(keyPrefix string) error {
 		prefix := []byte(keyPrefix)
 
 		for key, _ := cursor.Seek(prefix); bytes.HasPrefix(key, prefix); key, _ = cursor.Next() {
-			_ = bucket.Delete([]byte(key))
+			_ = bucket.Delete(key)
 		}
 		return nil
 	})