cleanup(setup_board): Remove /etc/make.conf.board
cleanup(setup_board): Remove /etc/make.conf.board

This file mostly just defined BINHOSTs but I'd like to move that
completely into coreos-overlay as the SDK BINHOSTs have always been. It
also sourced src/overlays/overlay-amd64-generic/make.conf but I want to
move the few things it defined into coreos-overlay as well.

The one interesting thing this file did was to optionally define
ACCEPT_LICENSE but that can go into /etc/make.conf.board_setup instead.

Overall this takes a chunk out of the make.conf spaghetti. :)

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