drop the deprecated IApplicationLifetime retrieval and pragma suppres…

…sion; call app.UseWebJobsScriptHost()

src/Cli/func/Actions/HostActions/Startup.cs

@@ -157,12 +157,7 @@ public void Configure(IApplicationBuilder app)
                     }
                 });
             }
-#pragma warning disable CS0618 // IApplicationLifetime is obsolete
-            IApplicationLifetime applicationLifetime = app.ApplicationServices
-                .GetRequiredService<IApplicationLifetime>();
-
-            app.UseWebJobsScriptHost(applicationLifetime);
-#pragma warning restore CS0618 // Type is obsolete
+            app.UseWebJobsScriptHost();
         }
 
         private class ThrowingDependencyValidator : DependencyValidator