Hi Peter!
I think your are talking about a mobile ready theme on Moodle website, is that right?
If it's that right, you can hide it using CSS media queries, for example:
@media (max-width: 767px)
.block_site_main_menu {
display: none;
}
This will hide the main menu block when displays are smaller than 767 pixels wide.
You can hide all the blocks, or the ones you select.
However the real CSS it will depend on your theme so I cannot assure you that this exact CSS will work.
Cheers!
Pau