Add a CHANGELOG entry about ORA1 removal

CHANGELOG.md

+- Role: ora
+  - Remove the ora1 role as support for it was deprecated in Cypress.
+  - Removed dependencies on ora throughout the playbooks / vagrantfiles.
 - Role: edxapp
   - Removed XmlModuleStore from the default list of modulestores for the LMS.
   - EDXAPP_XML_MAPPINGS variable no longer exists by default and is not used by the edxapp role.