Revert "Update uscore.md"

This reverts commit 16a2404.

Author: v-rachitsh

articles/healthcare-apis/fhir/toc.yml

@@ -45,8 +45,6 @@ items:
     - name: Customer-managed keys
       expanded: false
       items:
-      - name: US Core
-        href: uscore.md
       - name: Configure customer-managed keys
         href: configure-customer-managed-keys.md
       - name: Customer-managed keys best practices