Remove docs-related change from changelog

This change is not packaged and will change for the whole docs site, not
just for the next released version of the Python package. As such, it is
out of place in this changelog.

Author: samueljsb

CHANGELOG.md

@@ -7,10 +7,6 @@ adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
 
-### Added
-
-- Search plugin for MkDocs
-
 ### Fixed
 
 - Ensure cleanup actions in `durable` always happen when the wrapped code raises an unexpected error.