Delete assignment block buttons

Hi All,

I have trying to delete my custom assignment block's buttons but it didnt work. I know its so basic but maybe because the assignment block is custom, the code samples that I tried didnt give me any solution.

Those buttons that I wanted to delete:

What I have done so far is :

I enhanced GET_OCA_T_TABLE method and delete the rt_actions table which didnt effect anything.

I also tried to add a new button to see what is gonna happen to the same method but it adds the button up here;