in my case i want to delete a column 'Status' ,my problem is that i can't remove it by preference in di.xml

the preference override it works fine with other methods but this method no , i dont know why

this file is Mymodule\Dealer\Block\Adminhtml\Dealer\Grid\Reports

protected function _prepareColumns()
    {
        $this->addColumn('m_increment_id', array(
            'header'       => __('Order #'),
            'width'        => '100',
            'index'        => 'm_increment_id',
            'filter_index' => 'main_table.increment_id',
        ));

        $this->addColumn('m_created_at', array(
            'header'       => __('Purchase On'),
            'index'        => 'm_created_at',
            'type'         => 'm_datetime',
            'filter_index' => 'main_table.created_at',
        ));

          //$this->addColumn('status', array(
           // 'header'       => __('Status'),
           // 'index'        => 'm_status',
           // 'filter_index' => 'main_table.status',
           // 'type'         => 'options',
            //'width'        => '70px',
//            'options'      => Mage::getSingleton('sales/order_config')->getStatuses(),
       // ));

        return parent::_prepareColumns();
    }

the file for override in di.xml

<preference for="\Amasty\Perm\Block\Adminhtml\Dealer\Grid\Reports"
                type="Mymodule\Dealer\Block\Adminhtml\Dealer\Grid\Reports" />

can anyone help me please ?