Removed the extra client app custom path. (#3102)

Author: yhwen

nvflare/private/fed/client/client_engine.py

@@ -152,12 +152,6 @@ def start_app(
             return f"{ERROR_MSG_PREFIX}: Client app does not exist. Please deploy it before starting client."
 
         app_custom_folder = os.path.join(app_root, "custom")
-        if os.path.isdir(app_custom_folder):
-            try:
-                sys.path.index(app_custom_folder)
-            except ValueError:
-                _remove_custom_path()
-                sys.path.append(app_custom_folder)
 
         self.logger.info("Starting client app. rank: {}".format(self.rank))