Remove the redundant include_search in mkdocs.yml

docs/mkdocs.yml

@@ -17,7 +17,6 @@ use_absolute_urls: true
 # theme: docker
 theme_dir: ./theme/mkdocs/
 theme_center_lead: false
-include_search: true
 
 copyright: Copyright © 2014, Docker, Inc.
 google_analytics: ['UA-6096819-11', 'docker.io']