HDRenderPipeline: Remove None mode of double sided

- IT have no sense and cause artifact

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Editor/Material/Lit/BaseLitUI.cs

     {
         protected static class StylesBaseLit
         {
-            public static GUIContent doubleSidedNormalModeText = new GUIContent("Normal mode", "This will modify the normal base on the selected mode. None: untouch, Mirror: Mirror the normal with vertex normal plane, Flip: Flip the normal");
+            public static GUIContent doubleSidedNormalModeText = new GUIContent("Normal mode", "This will modify the normal base on the selected mode. Mirror: Mirror the normal with vertex normal plane, Flip: Flip the normal");
             public static GUIContent depthOffsetEnableText = new GUIContent("Enable Depth Offset", "EnableDepthOffset on this shader (Use with heightmap)");
 
             // Displacement mapping (POM, tessellation, per vertex)
 
         public enum DoubleSidedNormalMode
         {
-           None,
            Mirror,
            Flip
         }
                 DoubleSidedNormalMode doubleSidedNormalMode = (DoubleSidedNormalMode)material.GetFloat(kDoubleSidedNormalMode);
                 switch (doubleSidedNormalMode)
                 {
-                    case DoubleSidedNormalMode.None:
-                        material.SetVector("_DoubleSidedConstants", new Vector4(1.0f, 1.0f, 1.0f, 0.0f));
-                        break;
-
                     case DoubleSidedNormalMode.Mirror: // Mirror mode (in tangent space)
                         material.SetVector("_DoubleSidedConstants", new Vector4(1.0f, 1.0f, -1.0f, 0.0f));
                         break;

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Material/LayeredLit/LayeredLit.shader

         [ToggleOff] _EnableBlendModePreserveSpecularLighting("Enable Blend Mode Preserve Specular Lighting", Float) = 1.0
 
         [ToggleOff] _DoubleSidedEnable("Double sided enable", Float) = 0.0
-        [Enum(None, 0, Mirror, 1, Flip, 2)] _DoubleSidedNormalMode("Double sided normal mode", Float) = 1
+        [Enum(Mirror, 0, Flip, 1)] _DoubleSidedNormalMode("Double sided normal mode", Float) = 1
         [HideInInspector] _DoubleSidedConstants("_DoubleSidedConstants", Vector) = (1, 1, -1, 0)
 
         [Enum(Subsurface Scattering, 0, Standard, 1)] _MaterialID("MaterialId", Int) = 1 // MaterialId.RegularLighting

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Material/LayeredLit/LayeredLitTessellation.shader

         [ToggleOff] _EnableBlendModePreserveSpecularLighting("Enable Blend Mode Preserve Specular Lighting", Float) = 1.0
 
         [ToggleOff] _DoubleSidedEnable("Double sided enable", Float) = 0.0
-        [Enum(None, 0, Mirror, 1, Flip, 2)] _DoubleSidedNormalMode("Double sided normal mode", Float) = 1
+        [Enum(Mirror, 0, Flip, 1)] _DoubleSidedNormalMode("Double sided normal mode", Float) = 1
         [HideInInspector] _DoubleSidedConstants("_DoubleSidedConstants", Vector) = (1, 1, -1, 0)
 
     	[Enum(Subsurface Scattering, 0, Standard, 1)] _MaterialID("MaterialId", Int) = 1 // MaterialId.RegularLighting

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Material/Lit/Lit.shader

         [ToggleOff] _EnableBlendModePreserveSpecularLighting("Enable Blend Mode Preserve Specular Lighting", Float) = 1.0
 
         [ToggleOff] _DoubleSidedEnable("Double sided enable", Float) = 0.0
-        [Enum(None, 0, Mirror, 1, Flip, 2)] _DoubleSidedNormalMode("Double sided normal mode", Float) = 1
+        [Enum(Mirror, 0, Flip, 1)] _DoubleSidedNormalMode("Double sided normal mode", Float) = 1
         [HideInInspector] _DoubleSidedConstants("_DoubleSidedConstants", Vector) = (1, 1, -1, 0)
 
         [Enum(UV0, 0, Planar, 4, TriPlanar, 5)] _UVBase("UV Set for base", Float) = 0

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Material/Lit/LitTessellation.shader

         [ToggleOff] _EnableBlendModePreserveSpecularLighting("Enable Blend Mode Preserve Specular Lighting", Float) = 1.0
 
         [ToggleOff] _DoubleSidedEnable("Double sided enable", Float) = 0.0
-        [Enum(None, 0, Mirror, 1, Flip, 2)] _DoubleSidedNormalMode("Double sided normal mode", Float) = 1
+        [Enum(Mirror, 0, Flip, 1)] _DoubleSidedNormalMode("Double sided normal mode", Float) = 1
         [HideInInspector] _DoubleSidedConstants("_DoubleSidedConstants", Vector) = (1, 1, -1, 0)
 
         [Enum(UV0, 0, Planar, 4, TriPlanar, 5)] _UVBase("UV Set for base", Float) = 0