Remove sysctl element from overcloud image
Remove sysctl element from overcloud image

We moved sysctl management under puppet and the old key
providing sysctl settings to os-apply-config is empty so this
change removes the element from the overcloud image.

  # os-apply-config --key sysctl --type raw --key-default ''
  #

Depends-On: I197eb6825b6e7dbc03640cdb16ea160dd83f7adb
Change-Id: Ic920d8f172f98a12a58035276815a41fe0654f4e
openstack/tripleo-common,openstack/tripleo-common