Remove `clear_collection`.

tensorpack/tfutils/collection.py

@@ -10,7 +10,6 @@ from contextlib import contextmanager
 
 __all__ = ['backup_collection',
            'restore_collection',
-           'clear_collection',
            'freeze_collection']
 
 
@@ -40,17 +39,6 @@ def restore_collection(backup):
         tf.get_collection_ref(k).extend(v)
 
 
-def clear_collection(keys):
-    """
-    Clear some collections.
-
-    Args:
-        keys(list): list of collection keys.
-    """
-    for k in keys:
-        del tf.get_collection_ref(k)[:]
-
-
 @contextmanager
 def freeze_collection(keys):
     """