WordPress WooCommerce Quantity Field
Remove the Quantity Field from a WooCommerce Product Page

Using the Option in the Product Data Metabox

To remove the quantity option in WooCommerce, go to your WooCommerce product page in the WordPress dashboard. Scroll down past the editor and you will find the Product Data metabox.
Go to Inventory and enable the checkbox near Sold individually. Doing so allows only one item to be bought in a single order.

Hit Update and refresh your product page. The quantity field is now disabled!