Fix warning in Helm

[mkysel]

Fix:

W0107 10:53:45.880709   72989 warnings.go:70] spec.template.spec.containers[0].env[11]: hides previous definition of "XMTPD_METRICS_ENABLE", which may be dropped when using apply
W0107 10:53:45.914361   72989 warnings.go:70] autopilot-default-resources-mutator:Autopilot updated Deployment default/xmtpd-api: defaulted unspecified 'cpu' resource for containers [xmtpd] (see http://g.co/gke/autopilot-defaults).
W0107 10:53:45.914435   72989 warnings.go:70] spec.template.spec.containers[0].env[10]: hides previous definition of "XMTPD_METRICS_ENABLE", which may be dropped when using apply

The cause was that we were hardcoding metrics and allowing the config to set them.

Metrics are used for the probes, so they should never be turned off by configuration