Certified GKH Gardening Expert
This will not be possible. Armillaria are persistent, and will not be killed, easily. Their "body" resides underground, and on/in the roots. What you are seeing are simply reproductive organs, as with all mushroom fruiting bodies. Your roots are fully colonized, which signals for the fungus to reproduce. The decline will be fast once fruiting starts. It may only take a few seasons to kill the shrub.
As a mushroom cultivator, this is why I WILL NOT produce these indoors, or out. My indoors trees would be obliterated.
From here, I would remove the shrub and as much of the root mass as you can. Treat the area with fungicides, or you may opt for boiling water. You'll need to water the area every day with it for a few weeks to ensure that you kill spores in the area, as well.
Do you best NOT to disturb them while removing them. This will cause spores to spread. Remove them carefully by plucking as close to the base as possible.
https://www.gardeningknowhow.com/plant-problems/disease/armillaria-root-rot-control.htm
