cleanup: remove orphaned comments referencing invisible context

- Remove dangling '# Justification: ...' comment after the module
  docstring in case_validator.py (leftover review note).
- Remove 'This replaces the definitions/ directory.' migration
  sentence from definitions.py docstring (the directory no longer
  exists in the repo, so the note refers to invisible history).

Fixes #1500.

Author: lb1192176991-lab

toolchain/mfc/case_validator.py

@@ -11,7 +11,6 @@
 - src/simulation/m_checker.fpp
 - src/post_process/m_checker.fpp
 """
-# Justification: Comprehensive validator covering all MFC parameter constraints
 
 import re
 from functools import lru_cache

toolchain/mfc/params/definitions.py

@@ -1,8 +1,6 @@
-"""
-MFC Parameter Definitions (Compact).
+"""MFC Parameter Definitions (Compact).
 
 Single file containing all ~3,300 parameter definitions using loops.
-This replaces the definitions/ directory.
 """
 
 import re