Remove code for making Windows builds

It's not used anymore and it never worker reliably. The Windows binaries
should be produced in cleaner environment, ideally on Windows.

Signed-off-by: Michal Čihař <michal@cihar.com>
Release today

Signed-off-by: Michal Čihař <michal@cihar.com>
Document changes

Signed-off-by: Michal Čihař <michal@cihar.com>