Delete a Friends Expense

[ellaharrasser]

Deletes an existing expense between friends.

• [x] An authenticated user is required for a successful response
• [x] Only the creator of the expense is authorized to delete
• [x] Expense record is removed from the database after the request
• [x] Successful response includes a message indicating a successful deletion
• [x] Error response with status 404 is given when an expense does not exist with the provided id