client/driver: remove unused const 'dockerPullProgressEmitInterval'
client/driver: remove unused const 'dockerPullProgressEmitInterval'

hashicorp/nomad,hashicorp/nomad,dvusboy/nomad,hashicorp/nomad,dvusboy/nomad,nak3/nomad,burdandrei/nomad,burdandrei/nomad,burdandrei/nomad,hashicorp/nomad,hashicorp/nomad,hashicorp/nomad,burdandrei/nomad,nak3/nomad,dvusboy/nomad,nak3/nomad,nak3/nomad,burdandrei/nomad,dvusboy/nomad,nak3/nomad,burdandrei/nomad,dvusboy/nomad,dvusboy/nomad,burdandrei/nomad,nak3/nomad,nak3/nomad,dvusboy/nomad