Add a global option for turning off shadows on transparencies to match what builtin deferred does.

Assets/ScriptableRenderPipeline/MobileRenderPipeline/ClassicDeferred/ClassicDeferredPipeline.cs

 	[SerializeField]
 	TextureSettings m_TextureSettings = TextureSettings.Default;
 	public bool UseLegacyCookies;
+	public bool TransparencyShadows;
 	public Mesh m_PointLightMesh;
 	public float PointLightMeshScaleFactor = 2.0f;
 	public Mesh m_SpotLightMesh;
 		cmd.SetGlobalFloat("_reflRootHdrDecodeExp", defdecode.y);
 
 		cmd.SetGlobalFloat ("_useLegacyCookies", UseLegacyCookies?1.0f:0.0f);
+		cmd.SetGlobalFloat ("_transparencyShadows", TransparencyShadows ? 1.0f : 0.0f);
 
 		context.ExecuteCommandBuffer(cmd);
 		cmd.Dispose();

Assets/ScriptableRenderPipeline/MobileRenderPipeline/ClassicDeferred/UnityStandardForwardMobile.cginc

 int g_numLights;
 int g_numReflectionProbes;
 int _useLegacyCookies;
+int _transparencyShadows;
 
 float4x4 g_mViewToWorld;
 float4x4 g_mWorldToView;        // used for reflection only
 
 	  		int shadowIdx = asint(gPerLightData[lightIndex].y);
 			[branch]
-			if (shadowIdx >= 0)
+			if (shadowIdx >= 0 && _transparencyShadows)
 			{
 				float shadow = GetDirectionalShadowAttenuation(shadowContext, vPw, 0.0.xxx, shadowIdx, 0.0.xxx);
 				atten *= shadow;
 
 			int shadowIdx = asint(gPerLightData[lightIndex].y);
 			[branch]
-			if (shadowIdx >= 0)
+			if (shadowIdx >= 0 && _transparencyShadows)
 			{
 				float shadow = GetPunctualShadowAttenuation(shadowContext, vPw, 0.0.xxx, shadowIdx, vLw);
 				atten *= shadow;
 
 			int shadowIdx = asint(gPerLightData[lightIndex].y);
 			[branch]
-			if (shadowIdx >= 0)
+			if (shadowIdx >= 0 && _transparencyShadows)
 			{
 				float shadow = GetPunctualShadowAttenuation(shadowContext, vPw, 0.0.xxx, shadowIdx, 0.0.xxx);
 				atten *= shadow;

Assets/TestScenes/MobileDeferredTest/ClassicDeferredPipeline.asset

     pointCookieSize: 128
     reflectionCubemapSize: 128
   UseLegacyCookies: 1
+  TransparencyShadows: 0
   m_PointLightMesh: {fileID: 10207, guid: 0000000000000000e000000000000000, type: 0}
   PointLightMeshScaleFactor: 2
   m_SpotLightMesh: {fileID: 4300000, guid: 93e85ba57f65145538a8ac97bd005d40, type: 3}