Remove outdated Enabling Role-Based Access Control Using XACML documentation.

[tharindu1st]

Remove outdated doc [1]

[1] - https://apim.docs.wso2.com/en/latest/api-security/runtime/authorization/role-based-access-control-using-xacml/

[tharindu1st]

@wso2-engineering-bot create a PR for this issue following repo conventions

[tharindu1st]

@wso2-engineering-bot remove en/docs/api-security/runtime/authorization/role-based-access-control-using-xacml.md file as well.