Fix some typing issue in generate_default_trace (#390)

This patch removes an outdated comment (related to importing typing
annotations and then leaving everything in strings to a lack of support
from tooling at the time), removes a pylint disabled error as it no
longer applies, replace one string type with the actual type as it
should work now, and removes one no longer used type definition.

compiler_opt/tools/generate_default_trace.py

@@ -18,7 +18,7 @@
 import contextlib
 import functools
 import re
-from typing import Dict, List, Optional, Union, Tuple  # pylint:disable=unused-import
+from typing import Dict, List, Optional, Tuple
 
 from absl import app
 from absl import flags
@@ -38,9 +38,6 @@
 
 from tf_agents.system import system_multiprocessing as multiprocessing
 
-# see https://bugs.python.org/issue33315 - we do need these types, but must
-# currently use them as string annotations
-
 _DATA_PATH = flags.DEFINE_string('data_path', None,
                                  'Path to folder containing IR files.')
 _POLICY_PATH = flags.DEFINE_string(
@@ -69,11 +66,6 @@
     'gin_bindings', [],
     'Gin bindings to override the values set in the config files.')
 
-ResultsQueueEntry = Union[Optional[Tuple[str, List[str],
-                                         Dict[str,
-                                              compilation_runner.RewardStat]]],
-                          BaseException]
-
 
 class FilteringWorker(worker.Worker):
   """Worker that performs a computation and optionally filters the result.