Remove changelog entry for reverted commit

I had to revert changes made for this CHANGELOG entry so this is no
longer valid. The change for this entry was removed in 2c02bc0a.

activerecord/CHANGELOG.md

@@ -1452,18 +1452,6 @@
 
     *Chris Sinjakli*
 
-*   Validation errors would be raised for parent records when an association
-    was saved when the parent had `validate: false`. It should not be the
-    responsibility of the model to validate an associated object unless the
-    object was created or modified by the parent.
-
-    This fixes the issue by skipping validations if the parent record is
-    persisted, not changed, and not marked for destruction.
-
-    Fixes #17621.
-
-    *Eileen M. Uchitelle*, *Aaron Patterson*
-
 *   Fix n+1 query problem when eager loading nil associations (fixes #18312)
 
     *Sammy Larbi*