Remove unused parameters in docs-metadata-release template

[benbp]

These parameters are unused, and it's causing some template validation errors against Azure/azure-sdk-tools#1585, which uses a more strict parameter checking syntax.

{"$id":"1","customProperties":{"ValidationResults":[{"result":"error","message":"/eng/pipelines/templates/stages/archetype-python-release.yml (Line: 182, Col: 42): Unexpected parameter 'TargetDocRepo'"},{"result":"error","message":"/eng/pipelines/templates/stages/archetype-python-release.yml (Line: 188, Col: 45): Unexpected parameter 'ServiceDirectory'"}]},"innerException":null,"message":"Could not queue the build because there were validation errors or warnings.","typeName":"Microsoft.TeamFoundation.Build.WebApi.BuildRequestValidationFailedException, Microsoft.TeamFoundation.Build2.WebApi","typeKey":"BuildRequestValidationFailedException","errorCode":0,"eventId":3000}

[weshaggard]

FYI @danieljurek this is just a small part of the clean-up we need to do for the docs processing once you refactor it for the daily packages as well.