Remove Update Install Source Custom Action (#42114)

### What does this PR do?
This PR removes the update install source custom action that was added in: #40511

### Motivation
https://datadoghq.atlassian.net/browse/WINA-1929

The custom action updated the install source after installing via MSI to use the fleet package name and msi path. This can potentially cause reinstalls to fail as MSI does not use the sourcelist path during reinstalls.

### Describe how you validated your changes
Since this is just removing a custom action, the existing e2e tests should ensure that the agent installs and uninstalls just fine.

### Additional Notes

Author: mrafi97

releasenotes/notes/fleet-automation-msi-update-install-source-edbfaccf24bece0f.yaml

@@ -574,6 +574,7 @@ func (s *testAgentUpgradeSuite) TestUpgradeWithLocalSystemUser() {
 
 // TestDowngradeWithMissingInstallSource tests that a downgrade will succeed even if the original install source is missing
 func (s *testAgentUpgradeSuite) TestDowngradeWithMissingInstallSource() {
+	s.T().Skip("Skipping test due to removal of update install source custom action")
 	// Arrange
 	s.setAgentConfig()
 	s.installCurrentAgentVersion()

test/new-e2e/tests/installer/windows/suites/agent-package/upgrade_test.go

@@ -59,12 +59,6 @@ public static ActionResult SetupInstaller(Session session)
             return Datadog.CustomActions.SetupInstallerCustomAction.SetupInstaller(session);
         }
 
-        [CustomAction]
-        public static ActionResult UpdateInstallSource(Session session)
-        {
-            return Datadog.CustomActions.UpdateInstallSourceCustomAction.UpdateInstallSource(session);
-        }
-
         [CustomAction]
         public static ActionResult ReportFailure(Session session)
         {

tools/windows/DatadogAgentInstaller/AgentCustomActions/CustomAction.cs

@@ -70,7 +70,6 @@
   </ItemGroup>
   <ItemGroup>
     <Compile Include="APM\ApmConfigTests.cs" />
-    <Compile Include="InstallSource\InstallSourceTests.cs" />
     <Compile Include="InstallState\InstallStateTests.cs" />
     <Compile Include="InstallState\InstallStateTestSetup.cs" />
     <Compile Include="ProcessUserCustomActions\BaseProcessUserCustomActionsDomainTests.cs" />

tools/windows/DatadogAgentInstaller/CustomActions.Tests/CustomActions.Tests.csproj

@@ -96,7 +96,6 @@
     <Compile Include="ServiceCustomAction.cs" />
     <Compile Include="PatchInstallerCustomAction.cs" />
     <Compile Include="SetupInstallerCustomAction.cs" />
-    <Compile Include="UpdateInstallSourceCustomAction.cs" />
     <Compile Include="PythonDistributionCustomAction.cs" />
     <Compile Include="Extensions\SessionExtensions.cs" />
     <Compile Include="Interfaces\ISession.cs" />

tools/windows/DatadogAgentInstaller/CustomActions.Tests/InstallSource/InstallSourceTests.cs

@@ -20,8 +20,6 @@ public class AgentCustomActions
 
         public ManagedAction SetupInstaller { get; set; }
 
-        public ManagedAction UpdateInstallSource { get; set; }
-
         public ManagedAction EnsureGeneratedFilesRemoved { get; }
 
         public ManagedAction WriteConfig { get; }
@@ -322,23 +320,6 @@ public AgentCustomActions()
                 .SetProperties(
                     "PROJECTLOCATION=[PROJECTLOCATION], FLEET_INSTALL=[FLEET_INSTALL], DATABASE=[DATABASE]");
 
-            UpdateInstallSource = new CustomAction<CustomActions>(
-                    new Id(nameof(UpdateInstallSource)),
-                    CustomActions.UpdateInstallSource,
-                    Return.check,
-                    // The built-in RegisterProduct action normally sets the install source,
-                    // so our action must come after it to take effect.
-                    When.Before,
-                    Step.InstallFinalize,
-                    Conditions.FirstInstall | Conditions.Upgrading
-                )
-            {
-                Execute = Execute.deferred,
-                Impersonate = false
-            }
-                .SetProperties(
-                    "PROJECTLOCATION=[PROJECTLOCATION], FLEET_INSTALL=[FLEET_INSTALL], DATABASE=[DATABASE], AgentFlavor=[AgentFlavor]");
-
             // Cleanup leftover files on uninstall
             CleanupOnUninstall = new CustomAction<CustomActions>(
                     new Id(nameof(CleanupOnUninstall)),