Delete outdated md files that are already removed from the mkdocs.yml

[ashera96]

Description:

Following pages are outdated and those md files need to be removed. These don't belong to any any section in the documentation as they are not mentioned under the mkdocs.yml file.

• https://apim.docs.wso2.com/en/4.4.0/get-started/integration-quick-start-guide/
• https://apim.docs.wso2.com/en/4.4.0/install-and-setup/setup/setting-up-databases/working-with-the-resgistry/admin-working-with-users-roles-and-permissions/
• https://apim.docs.wso2.com/en/4.4.0/reference/connectors/db-event-inbound-endpoint/db-event-inbound-endpoint-example/#deploying-on-wso2-enterprise-integrator

Since these pages do exist, these documents show up in the search results and that can be misleading.