Answer

To remove an .msi from within another .msi, you should use a custom action to run msiexec.exe to perform the uninstall. 

Use the Execute Program from Destination to call an .msi within another .msi to perform uninstall:

1. Add an Execute Program from Destination custom action in the User Interface of MSI Script after CostFinalize.
2. The Execute Program from Destination custom action dialog appears. Fill in the following information:
   • Custom Action Name: Enter a name.
   • Working Directory: Enter SystemFolder
   • EXE and CommandLine: Enter the msiexec.exe /x {ProductCodeOfMSItoUninstall}
3. Accept all other defaults and click OK.

If you want the .msi to perform a silent uninstall, then add this following syntax in the EXE and CommandLine field.

msiexec.exe /i {ProductCodeOfMSItoUninstall} REMOVE="ALL" /q