[stable/chachet] remove DB_DRIVER duplication in configmap

[Becram]

Description

Since the variable is already defined at database.driver it causes duplication error in the configmap

Checklist

• [x] Title of the PR starts with chart name (e.g. [stable/mychartname])
• [x] I have read the contribution instructions, bumped chart version and regenerated the docs
• [x] Github actions are passing

[Becram]

as raised by https://github.com/deliveryhero/helm-charts/issues/385

[github-actions[bot]]

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