[BUG] Saved TwoTowerModel Query Block requires both item and user features as inputs

[jperez999]

Bug description

After training a two tower model, when you try to extract the user block (query tower) the model requires the both item and user features.

Steps/Code to reproduce bug

https://github.com/NVIDIA-Merlin/models/blob/poc/examples/POC/ItemRetrieval-TwoTower.ipynb
Run notebook through Save User Tower section and then check the query_tower object created with
query_tower.__dict__
You will see the extra item features in the model spec.

Expected behavior

Expect query block to only require the user features.

Additional context

This is blocking the end to end Ensemble API example.