Remove the envify command

Instead of using `kamal envify` to generate the .env file, we now assume
that it will be in place for us.

Options in place of `kamal envify`:
1. Pre-generate the .env file
2. Create the env file in the `.pre-init` hook
3. Log into a secret store/check you are logged in in the pre-init hook
   Then use .dotenv command and variable substitution to interpolate the
   secrets.

test/integration/broken_deploy_test.rb

@@ -4,8 +4,6 @@ class BrokenDeployTest < IntegrationTest
   test "deploying a bad image" do
     @app = "app_with_roles"
 
-    kamal :envify
-
     first_version = latest_app_version
 
     kamal :deploy