Hide Reassign button in the task

You just want to hide it or you want to remove the privilege itself.  If you don't want user to reassign a task go to Assignment tab where you can find set re-assignment privileges  set privilege to  No Privilege. If you just want to hide , I don't think we can do that. 

First you have to set the reassignment privileges to no privilege. This will hide the reassign button. But again if the user is a part of admin group, that reassign button will still show