Drop job step and Create\Update alert handlers (#636)

* Add Delete Job Step implementation

* Update create\update agent alert handlers to use execution handler

* Cleanup create/update/delete operator request handlers

src/Microsoft.SqlTools.ServiceLayer/Agent/Jobs/SqlServerAgentPropertiesAlertSystem.cs

@@ -1,3 +1,4 @@
+#if false
 //
 // Copyright (c) Microsoft. All rights reserved.
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
@@ -466,3 +467,4 @@ namespace Microsoft.SqlTools.ServiceLayer.Agent
         #endregion
     }
 }
+#endif