fix docs

PiperOrigin-RevId: 166919072

Author: Ryan Sepassi

docs/new_problem.md

@@ -162,8 +162,6 @@ from __future__ import print_function
 import os
 import tarfile # do we need this import
 
-import google3
-
 from tensor2tensor.data_generators import generator_utils
 from tensor2tensor.data_generators import problem
 from tensor2tensor.data_generators import text_encoder