usdImagingArnold not loading properly on linux

[cpichard]

Describe the bug
When using husk on linux, usdImaging will try to load usdImagingArnold as a plugin and fails as usdImagingArnold depends on libpxr_hdx which is not loaded by husk. As we don't really need hdx we should get rid of this dependencies.

[autodesk-oss-arnold-bot]

Issue synced internally to ARNOLD-13822