how can remove this element to avoid having two menu buttons with one that shows unnecessary pages

You can add this CSS code to hide that menu:

.secondary-navigation, .menu-toggle {
    display: none;
}

Of course, that option doesn’t remove it but just hide it.

To try to remove it, since I think you don’t want to get rid of the Max Mega Menu you can try to go to Appearance > Menus and find the menu on top and check if it has any Display location checkbox marked so you can uncheck it.

I didn’t find any options for a Secondary menu on its documentation so it’s kind of weird.