Remove duplicate "Custom Queries" title (#771)

Author: m98

docs/dom-testing-library/api-custom-queries.mdx

@@ -6,8 +6,6 @@ title: Custom Queries
 import Tabs from '@theme/Tabs'
 import TabItem from '@theme/TabItem'
 
-## Custom Queries
-
 `DOM Testing Library` exposes many of the helper functions that are used to
 implement the default queries. You can use the helpers to build custom queries.
 For example, the code below shows a way to override the default `testId` queries