Remove sed calls to replace KERBEROS_REALM as they are not needed any more when HBase is built against Hadoop 3

[soenkeliebau]

Description

In the past we built HBase against Hadoop 2.x, in which the Configuration object did not yet support the syntax for using environment variables in config files: ${env.VARNAME}

To work around this we added sed calls to do the replacement in the config files during container startup.

Since we now build HBase with Hadoop 3.x this functionality is now supported by HBase and we don't need these calls to sed anymore, as the placeholders will be replaced by HBase at runtime.

This PR removes the now unneeded calls.

Definition of Done Checklist

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# Author
- [x] Helm chart can be installed and deployed operator works
- [x] Integration tests passed (for non trivial changes)

# Reviewer
- [x] Code contains useful comments
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# Acceptance
- [x] Feature Tracker has been updated
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