Revert "mongodb performance improvement. Making index_creation as opt…

…ional"

This reverts commit 847b2a7.

libs/community/langchain_community/chat_message_histories/mongodb.py

@@ -32,7 +32,6 @@ def __init__(
         session_id: str,
         database_name: str = DEFAULT_DBNAME,
         collection_name: str = DEFAULT_COLLECTION_NAME,
-        index_creation:bool =True
     ):
         from pymongo import MongoClient, errors
 
@@ -48,8 +47,7 @@ def __init__(
 
         self.db = self.client[database_name]
         self.collection = self.db[collection_name]
-        if index_creation: #Conditional Index Creation for collection
-            self.collection.create_index("SessionId")
+        self.collection.create_index("SessionId")
 
     @property
     def messages(self) -> List[BaseMessage]:  # type: ignore