you seam to be asking 2 contradicting questions.
First you ask how to show an image in the cart, then ask how to remove the thumbnail column from the cart....
the thumbnail column is how you show the item image in the cart.
In the add to cart button behavior, you set the file name for the item image in the thumbnail cart column.
then in the cart display, you set the image folder for the thumbnail cart column, the cart display will handle the rest.
When adding the cart display, go to the second page, here you can add or remove cart columns from the display, you can select the thumbnail column and set the image folder.