HDRenderPipeline: Remove useless _BLENDMODE_SOFT_ADD

ScriptableRenderPipeline/Core/ShaderLibrary/Common.hlsl

 // The reason is that for compute shader we need to guarantee that the layout of CBs is consistent across kernels. Something that we can't control with the global namespace (uniforms get optimized out if not used, modifying the global CBuffer layout per kernel)
 
 // Structure definition that are share between C# and hlsl.
-// These structures need to be align on float4 to respectect various packing rules from sahder language.
+// These structures need to be align on float4 to respect various packing rules from sahder language.
 // This mean that these structure need to be padded.
 
 // Do not use "in", only "out" or "inout" as califier, not "inline" keyword either, useless.

ScriptableRenderPipeline/HDRenderPipeline/Material/LayeredLit/LayeredLit.shader

     #pragma shader_feature _HEIGHT_BASED_BLEND
     #pragma shader_feature _ _LAYEREDLIT_3_LAYERS _LAYEREDLIT_4_LAYERS
 
-    #pragma shader_feature _ _BLENDMODE_ALPHA _BLENDMODE_ADD _BLENDMODE_SOFT_ADD _BLENDMODE_MULTIPLY _BLENDMODE_PRE_MULTIPLY
+    #pragma shader_feature _ _BLENDMODE_ALPHA _BLENDMODE_ADD _BLENDMODE_MULTIPLY _BLENDMODE_PRE_MULTIPLY
 
     // This feature is only for transparent Lit
     #pragma shader_feature _ENABLE_FOG

ScriptableRenderPipeline/HDRenderPipeline/Material/LayeredLit/LayeredLitTessellation.shader

     #pragma shader_feature _HEIGHT_BASED_BLEND
     #pragma shader_feature _ _LAYEREDLIT_3_LAYERS _LAYEREDLIT_4_LAYERS
 
-    #pragma shader_feature _ _BLENDMODE_ALPHA _BLENDMODE_ADD _BLENDMODE_SOFT_ADD _BLENDMODE_MULTIPLY _BLENDMODE_PRE_MULTIPLY
+    #pragma shader_feature _ _BLENDMODE_ALPHA _BLENDMODE_ADD _BLENDMODE_MULTIPLY _BLENDMODE_PRE_MULTIPLY
 
     // This feature is only for transparent Lit
     #pragma shader_feature _ENABLE_FOG

ScriptableRenderPipeline/HDRenderPipeline/Material/Lit/Lit.shader

     #pragma shader_feature _THICKNESSMAP
     #pragma shader_feature _SPECULARCOLORMAP
 
-    #pragma shader_feature _ _BLENDMODE_ALPHA _BLENDMODE_ADD _BLENDMODE_SOFT_ADD _BLENDMODE_MULTIPLY _BLENDMODE_PRE_MULTIPLY
+    #pragma shader_feature _ _BLENDMODE_ALPHA _BLENDMODE_ADD _BLENDMODE_MULTIPLY _BLENDMODE_PRE_MULTIPLY
     
     // This feature is only for transparent Lit
     #pragma shader_feature _ENABLE_FOG

ScriptableRenderPipeline/HDRenderPipeline/Material/Lit/LitTessellation.shader

     #pragma shader_feature _THICKNESSMAP
     #pragma shader_feature _SPECULARCOLORMAP
 
-    #pragma shader_feature _ _BLENDMODE_ALPHA _BLENDMODE_ADD _BLENDMODE_SOFT_ADD _BLENDMODE_MULTIPLY _BLENDMODE_PRE_MULTIPLY
+    #pragma shader_feature _ _BLENDMODE_ALPHA _BLENDMODE_ADD _BLENDMODE_MULTIPLY _BLENDMODE_PRE_MULTIPLY
 
     // This feature is only for transparent Lit
     #pragma shader_feature _ENABLE_FOG

ScriptableRenderPipeline/HDRenderPipeline/Material/Material.hlsl

 // Blending
 //-----------------------------------------------------------------------------
 // This should match the possible blending modes in any material .shader file (lit/layeredlit/unlit etc)
-#if defined(_BLENDMODE_ALPHA) || defined(_BLENDMODE_ADD) || defined(_BLENDMODE_SOFT_ADD) || defined(_BLENDMODE_MULTIPLY) || defined(_BLENDMODE_PRE_MULTIPLY)
+#if defined(_BLENDMODE_ALPHA) || defined(_BLENDMODE_ADD) || defined(_BLENDMODE_MULTIPLY) || defined(_BLENDMODE_PRE_MULTIPLY)
 #define SURFACE_TYPE_TRANSPARENT
 #else
 #define SURFACE_TYPE_OPAQUE

ScriptableRenderPipeline/HDRenderPipeline/Material/Unlit/Editor/BaseUnlitUI.cs

-using System;
+using System;
 using UnityEngine;
 using UnityEngine.Experimental.Rendering.HDPipeline;
 using UnityEngine.Rendering;
             // These need to always been set either with opaque or transparent! So a users can swtich to opaque and remove the keyword correctly
             SetKeyword(material, "_BLENDMODE_ALPHA", false);
             SetKeyword(material, "_BLENDMODE_ADD", false);
-            SetKeyword(material, "_BLENDMODE_SOFT_ADD", false);
             SetKeyword(material, "_BLENDMODE_MULTIPLY", false);
             SetKeyword(material, "_BLENDMODE_PRE_MULTIPLY", false);
 

ScriptableRenderPipeline/HDRenderPipeline/Material/Unlit/Unlit.shader

 
     #pragma shader_feature _EMISSIVE_COLOR_MAP
 
-    #pragma shader_feature _ _BLENDMODE_ALPHA _BLENDMODE_ADD _BLENDMODE_SOFT_ADD _BLENDMODE_MULTIPLY _BLENDMODE_PRE_MULTIPLY
+    #pragma shader_feature _ _BLENDMODE_ALPHA _BLENDMODE_ADD _BLENDMODE_MULTIPLY _BLENDMODE_PRE_MULTIPLY
 
     // This feature is only for transparent Unlit
     #pragma shader_feature _ENABLE_FOG