We need to change it between release & nightly and it's probably
not much use for anyone else, and gets rid of the confusing errors
about the 'control' file not existing.
* Replace the windows signing script with certificateSubjectName
option which finds the right certificate from the smart card
* Remove the windows signing script as electron-builder does it
out-of-the-box on windows
* Remove the cert file which isn't necessary with native signing
None of this will work as it will need tweaking (at the very least
I've not copied the origin migrator because that's had long enough)
but these are files which already existed in their current state and
so don't need re-reviewing.
