Remove leftover skip_list file

This file contains name of files skipped during creation of the
rollback test delta. It does not need to be uploaded to the target.

Signed-off-by: Frédéric Dalleau <frederic.dalleau@collabora.com>

Jenkinsfile

@@ -272,6 +272,7 @@ def buildOStreeRollbackDelta(architecture, type, board, debosarguments = "", rep
         --add-metadata-string=ostree.collection-binding=${collection_id} \
         --bind-ref=${branch} \
         --skip-list="skip_list"
+      rm skip_list
       mkdir -p tests
       ostree --repo=${repo} static-delta generate \
         --from=${branch} \