Removed unused Opaque RT.

ScriptableRenderPipeline/LightweightPipeline/LWRP/LightweightPipeline.cs

         private RenderTargetIdentifier m_DepthRT;
         private RenderTargetIdentifier m_CopyDepth;
         private RenderTargetIdentifier m_Color;
-        private RenderTargetIdentifier m_OpaqueRT;
         private float[] m_OpaqueScalerValues = {1.0f, 0.5f, 0.25f, 0.25f};
 
         private float m_RenderScale;
             m_CopyColorRT = new RenderTargetIdentifier(CameraRenderTargetID.copyColor);
             m_DepthRT = new RenderTargetIdentifier(CameraRenderTargetID.depth);
             m_CopyDepth = new RenderTargetIdentifier(CameraRenderTargetID.depthCopy);
-            m_OpaqueRT = new RenderTargetIdentifier(CameraRenderTargetID.opaque);
             m_PostProcessRenderContext = new PostProcessRenderContext();
 
             m_CopyTextureSupport = SystemInfo.copyTextureSupport;