XROcclusionMesh.shader and XRMirrorView.shader are not stripped down when XR Plugin is not installed

To reproduce: 

1. Create a new project with URP samples;
2. Add only Cockpit Scene to the build settings;
3. Build for Android platform;
4. After building is complete, go to your project folder > Temp > shader-stripping.json;
5. Check what is the number of variants for Shaders/XR/XROcclusionMesh.shader and Shaders/XR/XRMirrorView.shader
    

Expected result: Number of variants is zero

Actual result: both shaders are not stripped even when XR Plugin is not installed