Put back typing for Base Runner create_shared_context

Summary:
Pull Request resolved: https://github.com/facebookresearch/d2go/pull/562

Reverting the changes introduced in the diff D46096375 to restore the state before modularization.

Reviewed By: tglik

Differential Revision: D46145093

fbshipit-source-id: 9897640ec00331fc6ea2817fa46b2272fc33cb8d

d2go/runner/default_runner.py

@@ -23,6 +23,7 @@ from d2go.data.utils import (
     maybe_subsample_n_images,
     update_cfg_if_using_adhoc_dataset,
 )
+from d2go.distributed import D2GoSharedContext
 from d2go.evaluation.evaluator import inference_on_dataset
 from d2go.modeling import ema
 from d2go.modeling.api import build_d2go_model
@@ -194,7 +195,7 @@ class BaseRunner(object):
         pass
 
     @classmethod
-    def create_shared_context(cls, cfg):
+    def create_shared_context(cls, cfg) -> D2GoSharedContext:
         """
         Override `create_shared_context` in order to run customized code to create distributed shared context that can be accessed by all workers
         """