Summary:
 

Yes the expense receipts associated with an expense sheet can be deleted without opening the expense sheet.

 
Resolution:
  1. Click on the Expense icon in the top menu.
  2. In the expense sheets for 'user name', you can see the list of open expense sheets.
  3. To edit the receipts of any of the listed expense sheets, click on "Receipt List" under 'Expense Receipts' section.
  4. In the 'Expense receipts' pop up box you can click on the "Delete image" under the 'Delete' section.