Remove Jenkins matrix job combination filter

Author: mark-vieira

.ci/jobs.t/elastic+elasticsearch+pull-request+packaging-tests-unix.yml

@@ -27,13 +27,6 @@
             - ':Delivery/Packaging'
           black-list-labels:
             - '>test-mute'
-    # these OSes are not supported past 7.x
-    execution-strategy:
-      combination-filter: |
-        (os!="centos-6-packaging" || ${ghprbTargetBranch}!="master") &&
-        (os!="debian-8-packaging" || ${ghprbTargetBranch}!="master") &&
-        (os!="oraclelinux-6-packaging" || ${ghprbTargetBranch}!="master") &&
-        (os!="ubuntu-16.04-packaging" || ${ghprbTargetBranch}!="master")
     axes:
       - axis:
           type: label-expression