unpin
Use this method to clear the list of pinned messages in a chat. If the chat is not a private chat, the bot must be an administrator in the chat for this to work and must have the 'can_pin_messages' administrator right in a supergroup or 'can_edit_messages' administrator right in a channel. Returns True on success.
Parameters
chat
Unique identifier for the target chat or username of the target channel (in the format @channelusername)