This reverts commit 57c3e1927c.
Drops --experimental-additional-egress-extproc-service and the
#ATE_MITM_EXTPROC_FILTER / #ATE_MITM_EXTPROC_CLUSTER markers, so
atenet-egress-with-sdsmint.yaml renders exactly as committed again
and hack/experimental-additional-egress-extproc.sh goes away.