promote-deployment: fix synchronize

Change I49afb49dd8301abec44c2aacddb8c62e73e0eb02 modified this to use
the upload-afs-synchronize role instead of a plain synchronize:.  This
role makes sure the flags are set correctly for copying to AFS.

However, it left behind the "delegate_to" which isn't valid with an
include_role; the job [1] is failing with

 ERROR! 'delegate_to' is not a valid attribute for a IncludeRole

Remove this.

[1] https://zuul.opendev.org/t/zuul/builds?job_name=opendev-promote-javascript-deployment

Change-Id: I5d817d61657a840f39359f24f6a9cd13e2238936

playbooks/artifacts/promote-deployment.yaml

@@ -54,7 +54,6 @@
         afs_source: '{{ src_dir }}/'
         afs_target: '{{ target_dir }}/'
         afs_copy_only: false
-      delegate_to: "{{ inventory_hostname }}"
     - name: Destroy AFS token
       include_role:
         name: destroy-afs-token