test_build_root: drop libcros checks
test_build_root: drop libcros checks

Nothing in the tree needs libcros anymore, so as a precursor to removing
that package, drop the root check on its version info.

BUG=chromium-os:15922
TEST=`cbuildbot arm-generic-full` works
TEST=`cbuildbot x86-generic-full` works

Change-Id: I03668c6dbb4cb79dbadb0c98e3c05dca01a8045d
Reviewed-on: https://gerrit.chromium.org/gerrit/18247
Reviewed-by: Chris Masone <98e3d65c6b0e9e2391eb4c2e8b1e572b77e544ed@chromium.org>
Commit-Ready: Mike Frysinger <8f3f75c74bd5184edcfa6534cab3c13a00a2f794@chromium.org>
Tested-by: Mike Frysinger <8f3f75c74bd5184edcfa6534cab3c13a00a2f794@chromium.org>

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