How to reproduce:
1. Create a new 3D template project
2. Open Package Manager and Import URP
3. Click Window -> Rendering -> Render Pipeline Converter
4. Click Initialize Converter button at the bottom left corner of the window
5. Observe the Material Upgrade section

Expected results: Converter should not detect internal URP package files as they are already bundled with the package
Actual results: Converter detects internal URP package files and suggests converting them

Reproducible with: 2021.2.0b1(12.0.0), 2021.2.0b6(12.0.0), 2022.1.0a4(12.0.0)
Could not test with: 2019.4.29f1, 2020.3.15f1, 2021.1.16f1, 2021.2.0a21(Converter window was not yet available)

Notes:
1. Proceeding to convert the Assets throws an error for every detected URP file as there is no upgrader to convert the shader to the selected pipeline