remove duplicated security context fields in mancenter-statefulset.yaml

[semihbkgr]

I removed the duplicated securityContext fields in mancenter-statefulset.yaml files.

{{- if .Values.securityContext.enabled }}
  securityContext:
    fsGroup: {{ .Values.securityContext.fsGroup }}
{{- end }}

These duplicated fields cause to error when building templates by kustomize.

mapping key "securityContext" already defined

see also #278

[devOpsHazelcast]

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[mtyazici]

@semihbkgr Could you also test the case where SecurityContext is removed from the values.yaml. I think it should give an error and to solve it we should use the if condition to check if the SecurityContext is enabled.

[mtyazici]

LGTM, thanks for the PR