hide the row headers

For now this is not possible. But you may change the source code to do that:

1) In function void GridTableColumnQuickButtonGraphic::paintEvent(QPainter& painter)

Please comment section:
/*
QPixmap icon(":res/quickbutton.png");
icon.setMask(icon.createMaskFromColor(Qt::magenta));
int xpos = rect().width() / 2 - icon.width() / 2;
int ypos = rect().height() / 2 - icon.height() / 2;
painter.drawPixmap(xpos, ypos, icon);
*/

2) Comment the contents of the functions:
void GridTableColumnQuickButtonGraphic::mousePressEvent(const QPoint& point, QMouseEvent* e)
{
}
void GridTableColumnQuickButtonGraphic::mouseReleaseEvent(const QPoint& point, QMouseEvent* e)
{
}

In the next update we will add the flag to control that behavior.

Have you insert in version 2.7 this flag? If yes, which method must i use?

This property was added to the version 2.8 of the grid.
GridTableViewOptions::setColumnsQuickMenuVisible(...) - for table view.
GridBandedTableViewOptions::setBandsQuickMenuVisible(...) - for banded table view.