Remove CHANGELOG.md entry that appears in 5-1-stable

This CHANGELOG.md is a continuation of the 5-1-stable one, there
shouldn't be any duplicate entries.

[ci skip]

activerecord/CHANGELOG.md

-*   Load only needed records on `ActiveRecord::Relation#inspect`.
-
-    Instead of loading all records and returning only a subset of those, just
-    load the records as needed.
-
-    Fixes #25537.
-
-    *Hendy Tanata*
-
 Please check [5-1-stable](https://github.com/rails/rails/blob/5-1-stable/activerecord/CHANGELOG.md) for previous changes.