The "Developer Edition" branding was not needed anymore because it was too easy to remove it. Also there are just minimal differences between the N950 firmware and the N9 firmware (some preinstalled Games, mostly) so there is no need to brand it as dev edition anymore.

The SDK installer was just the SDK installer file on the memory of the device. It is totally possible to download it now (wasn't the case when the devices were handed out) and that means that there is no need to distribute it using the firmware/devices.