Drop secure.yaml warning and sample file

Users following the deployment guide see the warning "There is
no file terraform/secure.yaml, create one by using
terraform/secure.yaml.sample as template" in their log output.
This is confusing because the guide recommends application
credentials, where the secret is already in clouds.yaml and no
secure.yaml is needed.

Remove the secure.yaml existence check from setup-testbed.py
and delete terraform/secure.yaml.sample. The check was already
non-fatal (warning + sleep, no exit) — a compromise from PR
#1879 where it was noted that secure.yaml is optional for app
credentials. A TODO to add smarter detection was left but never
followed up on.

The deployment guide now exclusively recommends application
credentials (osism/osism.github.io#972). For production
deployments, a more fine-grained check that validates
credentials based on auth type would still be valuable.

AI-assisted: Claude Code
Signed-off-by: Roger Luethi <luethi@osism.tech>

Author: ideaship

contrib/setup-testbed.py

@@ -7,7 +7,6 @@
 import sys
 import yaml
 import os
-import time
 
 
 def lookup(yaml_path: str, local_data: dict) -> None | str | dict:
@@ -48,14 +47,6 @@ def _check_file(filename: str, name: str):
         print(e)
         sys.exit(1)
 
-    # TODO: as discussed in https://github.com/osism/testbed/pull/1879 we add a app credential check later
-    # to make a smart distinction if that check is needed or not.
-    try:
-        _check_file("terraform/secure.yaml", cloud)
-    except Exception as e:
-        print(e)
-        time.sleep(2)
-
     sys.exit(0)