fix(bootstrap_sdk): Don't include cross toolchains in final tarball.
fix(bootstrap_sdk): Don't include cross toolchains in final tarball.

The packages have to be downloaded separately so don't waste space
including it in the stage4 tarball.

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