Update ocp-4-15-release-notes, since there is no plan to remove icsp in future release.

[bshaw7]

SInce there is no plan to remove ICSP object hence we need to update the release notes accordingly.

From this: Using an ICSP object to configure repository mirroring is a deprecated feature. Deprecated functionality is still included in OpenShift Container Platform and continues to be supported; however, it will be removed in a future release of this product and is not recommended for new deployments.

To this: Using an ICSP object to configure repository mirroring is a deprecated feature. Deprecated functionality is still included in OpenShift Container Platform and continues to be supported; however, It might be removed in a future release of this product. Because it is deprecated functionality, avoid using it for new deployments.

Version(s): 4.13, 4.14, 4.15

Issue: https://issues.redhat.com/browse/OCPBUGS-36519

Link to docs preview: https://docs.redhat.com/en/documentation/openshift_container_platform/4.15/html/release_notes/ocp-4-15-release-notes#ocp-4-15-nodes-icsp-idms-compatibility

OpenShift Container Platform 4.15 release notes > 1.3. New features and enhancements > 1.3.17. Nodes > 1.3.17.3. ICSP, IDMS, and ITMS are now compatible

QE review: