Remove built-in render pipeline support

I am trying to test a table using Unity's built-in render pipeline, but balls don't seem to be working currently. According to [the documentation](https://docs.visualpinball.org/creators-guide/setup/installing-vpe.html): "the built-in renderer is legacy not recommended", but I see no mention if it not being supported.

**Unity version:** 2022.3.6f1

**Steps to reproduce:**
- Create a new Unity project with the 3D template
- Install VPE packages:
- org.visualpinball.engine.unity
- org.visualpinball.unity.assetlibrary
- org.visualpinball.engine.pinmame
- Save a default .vpx table from VPX
- Import .vpx into VPE using Visual Pinball > Editor > Import Wizard
- Enter Play mode
- Pressing/holding Enter doesn't launch a ball