WIX installer: add_vs_tool action run on uninstall

[derekbruening]

Xref #1620

There's something wrong with the "NOT Installed AND NOT REMOVE" trigger for the add_vs_tool action in the WIX installer. If you make it Return="check" you can see that it tries to run it on uninstall! You end up with this error:

"There is a problem with this Windows Installer package. A program required for this install to complete could not be run."

Event log says: Product: Dr. Memory -- Error 1721. There is a problem with this Windows Installer package. A program required for this install to complete could not be run. Contact your support personnel or package vendor. Action: add_vs_tool, location: C:\Program Files (x86)\Dr. Memory\bin\vs_external_tool.exe, command: "C:\Program Files (x86)\Dr. Memory\bin\drmemory.exe"

For now this is set so we ignore the failure but it would be nice to understand and fix.