You can't remove it from the text-based email receipts, only from the shopper email receipts if you enable HTML receipts by checking the checkbox at the top of the Commerce Setup -> Order System -> Thank You menu labeled 'Customer E-mail Receipt in HTML format'. Then the HTML of the receipt is formated based on the [-- DEFINE ThankYou_Email --] section of the shopping cart template.
The tag in this template that creates the table of products is [-- SC_Cart --]. You can add specific parameters to this tag to exclude certain columns or you can re-order them. The tag with all available parameters looks like this:
[-- SC_Cart delete quantity image name sku price total --]
So to not include the SKU column you would specify the SC_Cart tag like this but leave out the sku parameter.
Documentation for this shopping cart template tag can be found in the shopping cart custom template tag specs at:
http://www.shopsite.com/help/9.0/en-US/sc/pro/custom.template.spec-sc.html
-Loren