Fix duplicate readonly field in opensign.yaml

Removed duplicate 'readonly' field and ensured proper formatting.

Author: prafull-opensignlabs

docs/docs/API-docs/v1.1/opensign.yaml

@@ -1752,7 +1752,6 @@ paths:
           "default": "11-05-2025",
           "min_date": "",
           "max_date": "",
-          "readonly": false,
           "signing_date": false
         }
         ```