Remove METRICS_MONGOENGINE_ALIAS and MetricsMongoResource
Fixes #2210 

- This PR removes METRICS_MONGOENGINE_ALIAS and MetricsMongoResource along with its references
Remove METRICS_MONGOENGINE_ALIAS and MetricsMongoResource: Fixes #2210 

- This PR removes METRICS_MONGOENGINE_ALIAS and MetricsMongoResource along with its references