vendor/ must be removed first, otherwise files added to vendor/ that aren't added to
vendor.conf will not cause the validation to fail.
Signed-off-by: Daniel Nephin <dnephin@gmail.com>
The DCO check is primarily only relevant as part of CI, so it
doesn't need to be in the Makefile. A contributor looking to
validate their commits can run script/validate/dco.
Signed-off-by: Daniel Nephin <dnephin@gmail.com>
