some renaming

mmdet/core/__init__.py

-from .rpn_ops import *  # noqa: F401, F403
+from .anchor import *  # noqa: F401, F403
 from .bbox_ops import *  # noqa: F401, F403
 from .mask_ops import *  # noqa: F401, F403
 from .losses import *  # noqa: F401, F403

mmdet/core/utils/__init__.py

 from .dist_utils import (init_dist, reduce_grads, DistOptimizerHook,
                          DistSamplerSeedHook)
-from .hooks import EmptyCacheHook
 from .misc import tensor2imgs, unmap, multi_apply
 
 __all__ = [
     'init_dist', 'reduce_grads', 'DistOptimizerHook', 'DistSamplerSeedHook',
-    'EmptyCacheHook', 'tensor2imgs', 'unmap', 'multi_apply'
+    'tensor2imgs', 'unmap', 'multi_apply'
 ]

mmdet/core/utils/hooks.py

-import torch
-from mmcv.runner import Hook
-
-
-class EmptyCacheHook(Hook):
-
-    def before_epoch(self, runner):
-        torch.cuda.empty_cache()
-
-    def after_epoch(self, runner):
-        torch.cuda.empty_cache()