When you switched to Philips Hue without SmarthThings hub - it changed from a direct connection to a cloud to cloud integration so that will explain the hue bridge not showing in IDE.
Those are not currently available (to my knowledge with either of the two official hue integrations.
To remove the hue b smartapp, you would need to remove all the hue devices first that it installed, then remove the hue b smartapp within the ST app in the Automations section. If it does not appear in the main screen, click on Add Routine, tap the Discover tab, scroll down to the custom smartapps section. After that is removed, you can remove the custom code in IDE for hue b.
The hue bridge needs to be on the same subnet as your ST hub. You also may need to press the button on the hue bridge when you start the add device process in the ST app. If still not found, restart your router.
I imagine the reason it was not discovered was the hue b smartapp that was installed and currently connected.
There is also a community developed Edge Driver for Hue that you can check out.