Removed mongodbmulti CRD from helm chart (#221)

# Summary

This removes old, unnecessary CRD from the helm chart.

MongoDBMulti was renamed to MongoDBMultiCluster just before GA of multi
cluster and it should not be there anymore.

We also don't publish it to the OLM bundles:
https://github.com/redhat-openshift-ecosystem/certified-operators/blob/main/operators/mongodb-kubernetes/1.1.0/manifests/mongodb-kubernetes.clusterserviceversion.yaml

Author: lsierant