Disable focus stealing prevention

Following on from the discussion in gnome-shell#358 (closed) and gtk#624 (closed), focus stealing prevention should be removed or disabled until a robust means of making it Just Work™ is found, because per comments in gtk#624 (closed) and from bug reports such as geary#482 (closed), it's clear that a number of people including both app developers and people using GNOME consider the current focus stealing prevention mechanism a bug, not a feature.

Specifically, the requirement that applications pass GDK event timestamps around so as to avoid the "Blah is ready" notification is impossible for applications to meet. Many blessed and commonly used GNOME APIs and libraries don't provide access to GDK event timestamps, including but not limited to GAction and all of its uses, and WebKitGTK. Further, third party applications use arbitrary toolkits that suffer the same problem. I don't know of Qt's status, but applications based on Electron for example all exhibit this problem because that toolkit does not provide API for obtaining a timestamp, let alone passing a timestamp in.

So until some way to address this in general in found, focus stealing prevention should be disabled to fix what in the end is a much larger usability problem than the original problem it was designed to fix.