Bug 1169944 - Remove requirements/prod.txt since it contains no packages

We had to do at least one deploy after the initial landing of
bug 1169944, before removing prod.txt, to avoid errors during update.py.
That has now occurred, so we can remove the file.

.landscape.yaml

@@ -10,7 +10,6 @@ uses:
   - celery
 requirements:
   - requirements/common.txt
-  - requirements/prod.txt
   - requirements/dev.txt
 ignore-paths:
   - .git

requirements/prod.txt

@@ -1,5 +0,0 @@
-# This Source Code Form is subject to the terms of the Mozilla Public
-# License, v. 2.0. If a copy of the MPL was not distributed with this
-# file, you can obtain one at http://mozilla.org/MPL/2.0/.
-
-# Delete this file once we've done at least one deploy after bug 1169944 (since update.py needed updating)