build_image: when generating update payload don't generate metadata
build_image: when generating update payload don't generate metadata

This feature was removed from delta_generator.

vmware/coreos-scripts,nicescale/scripts,marineam/coreos-scripts,BugRoger/scripts,mischief/scripts,gtank/scripts,BugRoger/scripts,sigma/coreos-scripts,sigma/coreos-scripts,fivethreeo/scripts,trnubo/scripts,marineam/coreos-scripts,andrejro/coreos--scripts,smilart/scripts,zhang0137/scripts,coreos/scripts,zhang0137/scripts,smilart/scripts,endocode/scripts,trnubo/scripts,vmware/coreos-scripts,smilart/scripts,gtank/scripts,nicescale/scripts,mischief/scripts,mjg59/scripts,marineam/coreos-scripts,gtank/scripts,coreos/scripts,BugRoger/scripts,mjg59/scripts,endocode/scripts,andrejro/coreos--scripts,glevand/coreos--scripts,mischief/scripts,endocode/scripts,fivethreeo/scripts,fivethreeo/scripts,nicescale/scripts,trnubo/scripts,glevand/coreos--scripts,sigma/coreos-scripts,andrejro/coreos--scripts,vmware/coreos-scripts,zhang0137/scripts,mjg59/scripts