remove useless method

mmdet/api/train.py

 from __future__ import division
 
-import random
 from collections import OrderedDict
 
-import numpy as np
 import torch
 from mmcv.runner import Runner, DistSamplerSeedHook
 from mmcv.parallel import MMDataParallel, MMDistributedDataParallel
@@ -45,13 +43,6 @@ def batch_processor(model, data, train_mode):
     return outputs
 
 
-def set_random_seed(seed):
-    random.seed(seed)
-    np.random.seed(seed)
-    torch.manual_seed(seed)
-    torch.cuda.manual_seed_all(seed)
-
-
 def train_detector(model,
                    dataset,
                    cfg,