Microsoft has ended support for Windows Phone 8.1, the operating system that powers around 75% of Windows smartphones in the wild today. The curtain is being drawn on a disastrous attempt to expand Windows from its PC roots, using the $7.2bn acquisition of Nokia’s handset division as a springboard – which ultimately led to Microsoft writing off over $8bn of that investment. Nokia is now back in the handset market, at least indirectly, but Microsoft has now given up entirely on the platform side of things, both in terms of devices and the OS that powers them. Instead, its mobile strategy is now centered around its Office applications, and Skype – although recent updates have received a lot of strong…