Fixes "linkifiedText" error when cancelling message

[samuelchristlie]

Removing linkifiedText fixes #81. I'm not sure what it does or if it's required at all, since it's not used in any other part of the code. Performing a network analysis on Poe gives the following request JSON, which has no mention of linkifiedText:

{"queryName":"stopMessage_messageCancel_Mutation","variables":{"messageId":xxx,"textLength":xxx},"extensions":{"hash":"xxx"}}

Removing linkifiedTextLength from line 900 in api.py fixes my problem

variables = {"messageId": chunk["messageId"], "textLength": len(chunk["text"]), "linkifiedTextLength": len(chunk["linkifiedText"])}

[snowby666]

Theres a syntax error with the spare ")" at the end.