windows: remove outdated installation instructions

artiq-fast/windows/install.txt

@@ -1,13 +0,0 @@
-Add user account with expected password [user/user].
-Enable the OpenSSH server:
-- "Add or remove programs"
-- "Manage optional features"
-- "Add a feature"
-- "OpenSSH Server"
-- "Install"
-- Open "Services"
-- Double-click the "OpenSSH SSH Server" service
-- Set "Startup type" to "Automatic"
-- "Start"
-- "Ok"
-Then press ENTER here to proceed with automatic installation