Delete Release Branch Sync workflow

Starting with FR5 we no long rely on the specific release sync
branch. Lets remove the job.

Jira: OSPRH-25747

Signed-off-by: Martin Schuppert <mschuppert@redhat.com>

# Please enter the commit message for your changes. Lines starting
# with '#' will be kept; you may remove them yourself if you want to.
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# On branch delete_release_branch_sync
# Changes to be committed:
#	deleted:    .github/workflows/release-branch-sync.yaml
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# Untracked files:
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#	2
#	IMPLEMENTATION_SUMMARY.md
#	TEST1_IMPROVEMENTS.md
#	TEST2_FIXES_TODO.md
#	TEST2_WEBHOOK_FIX.md
#	api/core/v1beta1/SERVICE_NAME_CACHING.md
#	backups/
#	building-test-catalog-for-upgrades.md
#	galerabackup-cell1.yaml
#	galerabackup.yaml
#	galerarestore-cell1.yaml
#	galerarestore.yaml
#	hack/pin-bundle-images.sh.bk
#	must-gather.local.3061536808181834403/
#	openstack-catalog-clean.Dockerfile
#	openstack-catalog-clean/
#	openstack-catalog.Dockerfile
#	openstack-catalog/
#	t.yaml
#	tt.yaml
#	webhook-backup.yaml
#	webhook-backup2.yaml
#

Author: stuggi