refactor: Remove dict_with_str_keys().

This function is no longer needed in python3, as it was decoding
keys that already came for a JSON-decoded string.

zerver/lib/message.py

@@ -15,7 +15,6 @@ from zerver.lib.cache import (
     to_dict_cache_key_id,
 )
 from zerver.lib.request import JsonableError
-from zerver.lib.str_utils import dict_with_str_keys
 from zerver.lib.stream_subscription import (
     get_stream_subscriptions_for_user,
 )
@@ -111,7 +110,7 @@ def sew_messages_and_reactions(messages, reactions):
 
 def extract_message_dict(message_bytes):
     # type: (bytes) -> Dict[str, Any]
-    return dict_with_str_keys(ujson.loads(zlib.decompress(message_bytes).decode("utf-8")))
+    return ujson.loads(zlib.decompress(message_bytes).decode("utf-8"))
 
 def stringify_message_dict(message_dict):
     # type: (Dict[str, Any]) -> bytes

zerver/lib/str_utils.py

@@ -66,11 +66,6 @@ def force_str(s, encoding='utf-8'):
     else:
         raise TypeError("force_str expects a string type")
 
-def dict_with_str_keys(dct, encoding='utf-8'):
-    # type: (Mapping[NonBinaryStr, Any], str) -> Dict[str, Any]
-    """applies force_str on the keys of a dict (non-recursively)"""
-    return {force_str(key, encoding): value for key, value in dct.items()}
-
 class ModelReprMixin:
     """
     This mixin provides a python 2 and 3 compatible way of handling string representation of a model.