Remove redundant input addition in workflows

The code change deletes the line where the messageInput is added to the Inputs list of the builder in the `Workflows.cs` file, since this operation is redundant. The input is automatically added during its creation and doesn't need an explicit addition, thus improving code efficiency.

test/integration/Elsa.IntegrationTests/Serialization/ProgrammaticWorkflowsAndDelegates/Workflows.cs

@@ -14,7 +14,6 @@ protected override void Build(IWorkflowBuilder builder)
         var messageInput = builder.WithInput<string>("Message", "The message to write to the console.");
 
         builder.Name = "Greeter Workflow";
-        builder.Inputs.Add(messageInput);
         builder.Root = new WriteLine(context => context.GetInput<string>(messageInput));
     }
 }