Revert "Add Upgrade handler to upgrade from 7.2 to 7.3"

This reverts commit 2498ec9.

Author: alex-kulakov

Orm/Xtensive.Orm.Tests/Upgrade/LegacyUpgrade/GeneratorUpgrade/Model.cs

@@ -13,11 +13,6 @@
 
 namespace Xtensive.Orm.Tests.Upgrade.LegacyUpgrade.GeneratorUpgrade
 {
-  public class CustomUpgrdeHandler: UpgradeHandler
-  {
-    public override bool CanUpgradeFrom(string oldVersion) => true;
-  }
-
   namespace ReferenceModel.Part1
   {
     [HierarchyRoot]

Orm/Xtensive.Orm.Tests/Upgrade/LegacyUpgrade/GeneratorUpgrade/SimpleSchemaTest.cs

@@ -433,15 +433,13 @@ protected virtual void InitializeGenerators(DomainConfiguration configuration, l
 
     private void CreateDb(bool defaultGeneratorSettings, bool lessGenerators = false, long seedIncrease = 0, long cacheSizeIncrease = 0)
     {
-      var config = BuildDomainConfiguration().Clone();
-      config.Types.Register(typeof(CustomUpgrdeHandler));
+      var config = BuildDomainConfiguration();
+      var driver = TestSqlDriver.Create(config.ConnectionInfo);
 
       // clean db - deletes all the tables except for metadata tables
       // tables from previous tests are unpredictable and this is reliable thought expensive way of cleaning :-)
       using (var domain = Domain.Build(config)) { }
 
-      var driver = TestSqlDriver.Create(config.ConnectionInfo);
-
       //complete removal
       using (var connection = driver.CreateConnection()) {
         connection.Open();