Delete an Image for a Spot

[Lillith13]

Delete an existing image for a Spot.

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

[Lillith13]

• [ ] test endpoint