chore: delete workflows for milestones (#79)

On-behalf-of: Gerald Morrison (SAP) <gerald.morrison@sap.com>

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#### What this PR does / why we need it
delete workflow for milestones as it does not work propoerly in the new
dev setup only using forks.

Signed-off-by: Gerald Morrison (SAP) <gerald.morrison@sap.com>
Co-authored-by: Gerald Morrison (SAP) <gerald.morrison@sap.com>

Author: morri-son