Revert "Asset slave should delete files removed on master"
Revert "Asset slave should delete files removed on master"

This reverts commit 23221e6ac0392dfdf2f2a0c3799c2aa037f75129.

I've realised that this is potentially dangerous should the nfs mount
fail on slave, as it would wipe out the backup directory.

I'm adding a script to do this more carefully.

alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet