[FIX] project_timesheet: remove useless overwrite

It was doing something before but the useful line was removed at 908f4165
The method is no longer useful and can be removed.
It was error prone has it had not the same signature as the one on project.
Fixes #13402

addons/project_timesheet/project_timesheet.py

@@ -122,15 +122,6 @@ class task(osv.osv):
             vals[task.id]['planned_hours'] += task.effective_hours
         return vals
 
-    def onchange_project(self, cr, uid, ids, project_id, context=None):
-        result = super(task, self).onchange_project(cr, uid, ids, project_id, context=context)
-        if not project_id:
-            return result
-        if 'value' not in result:
-            result['value'] = {}
-        project = self.pool['project.project'].browse(cr, uid, project_id, context=context)
-        return result
-
 
 class res_partner(osv.osv):
     _inherit = 'res.partner'