Revert " Moved PBR materials folder. Added a copy of SkyEnvironment to Lightweight."

This reverts commit c48c439359a5f0c4e738f443557e7e6c068e9d26.

Assets/Tests/GraphicsTests/RenderPipeline/LightweightPipeline/Scenes/Materials/PBR/Sky.mat

         m_Scale: {x: 1, y: 1}
         m_Offset: {x: 0, y: 0}
     - _Tex:
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+        m_Texture: {fileID: 8900000, guid: 9c13f7d97fda704439868458dc2385ed, type: 3}
         m_Scale: {x: 1, y: 1}
         m_Offset: {x: 0, y: 0}
     m_Floats:

Assets/Tests/GraphicsTests/RenderPipeline/LightweightPipeline/Assets/HDRI.meta

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Assets/Tests/GraphicsTests/RenderPipeline/LightweightPipeline/Scenes/Materials/PBR/Metals.meta

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Assets/Tests/GraphicsTests/RenderPipeline/LightweightPipeline/Scenes/Materials/PBR/Spheres.meta

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Assets/Tests/GraphicsTests/RenderPipeline/LightweightPipeline/Scenes/Shaders/StandardPBRShader/Metals.unity.meta

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