Replica Count isn't used

Summary

https://repo1.dso.mil/platform-one/big-bang/apps/collaboration-tools/mattermost/-/blob/main/chart/values.yaml#L40

This value isn't used as part of the mattermost configuration

❯ k get pods -n mattermost
NAME                         READY   STATUS    RESTARTS   AGE
mattermost-postgresql-0      1/1     Running   1          62m
minio-2                      1/1     Running   2          62m
minio-0                      1/1     Running   2          62m
minio-1                      1/1     Running   2          62m
mattermost-9cb9f7878-5dlrp   1/1     Running   1          62m