Remove uses of Quotient:Omittable

Note this technically won't build for now because of the lack of RoomMember support but I'll push that at the quotient-next branch next. 

This is needed as well to get a branch that builds on dev.

src/jobs/neochatdeletedevicejob.h

@@ -9,5 +9,5 @@
 class NeochatDeleteDeviceJob : public Quotient::BaseJob
 {
 public:
-    explicit NeochatDeleteDeviceJob(const QString &deviceId, const Quotient::Omittable<QJsonObject> &auth = Quotient::none);
+    explicit NeochatDeleteDeviceJob(const QString &deviceId, const Quotient::Omittable<QJsonObject> &auth = {});
 };