Remove stack from default paas manifest
Remove stack from default paas manifest

Setting 'stack' in the manifest makes `cf push` raise an error
(The app is invalid: Lifecycle type cannot be changed) when pushing
to a docker app that already exists.

Removing 'stack' solves the issue.

alphagov/digitalmarketplace-aws,alphagov/digitalmarketplace-aws,alphagov/digitalmarketplace-aws