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/accessory_test.rb

@@ -2,8 +2,6 @@ require_relative "integration_test"
 
 class AccessoryTest < IntegrationTest
   test "boot, stop, start, restart, logs, remove" do
-    kamal :envify
-
     kamal :accessory, :boot, :busybox
     assert_accessory_running :busybox