That'll remove it from every page I just wanted remove it from chat page

you need put that code in the chat plugin  
not admin theme edit

Can you show me how to do that?

i dont have that plugin sorry  

you could simple remove it in language 

I've removed it by removing the line $this->setPageHeading("Chat");. Just wanted to utilise the maximum space and increase the height of chat area without making the page heigh too long