chore: remove outdated code comment

Resolves:
  - solana-foundation#333 (comment)

The comment mentioned 'Deep addon configuration validation' but the module
doesn't implement any addon configuration validation.

Author: cds-amal

crates/txtx-test-utils/src/simple_validator.rs

@@ -5,7 +5,6 @@
 //! ## Known Limitations
 //!
 //! 1. Circular dependency detection between actions is not implemented
-//! 2. Deep addon configuration validation only checks for presence of fields
 
 use crate::addon_registry::{extract_addon_specifications, get_all_addons};
 use crate::builders::ValidationResult;