MSI: only allow one version (64-bit or 32-bit) to be installed

src/windows/installer/Product.wxs

 <?define ProductName = "eSpeak NG Text-to-Speech" ?>
 <?if $(var.Platform) = x64 ?>
 <?define ProductDisplayName = "$(var.ProductName) 64-bit" ?>
-<?define ProductId = "3DA6DF03-E5CD-4A93-B06F-707484742BAB" ?>
-<?define ProductUpgradeCode = "B4F779EB-AC6C-49D2-A12D-4871E4520C0F" ?>
 <?define Win64 = "yes" ?>
 <?define PlatformProgramFilesFolder = "ProgramFiles64Folder" ?>
 <?else ?>
 <?define ProductDisplayName = "$(var.ProductName)" ?>
-<?define ProductId = "4B445D11-6C40-474A-AF7C-CBF5CC8D8F62" ?>
-<?define ProductUpgradeCode = "53330FEC-30DA-438A-B4B7-E43EAA62F43F" ?>
 <?define Win64 = "no" ?>
 <?define PlatformProgramFilesFolder = "ProgramFilesFolder" ?>
 <?endif ?>
 <Wix xmlns="http://schemas.microsoft.com/wix/2006/wi">
-  <Product Id="$(var.ProductId)" Name="$(var.ProductDisplayName)" Language="1033" Version="1.48.15.0" Manufacturer="Cainteoir Technologies" UpgradeCode="$(var.ProductUpgradeCode)">
+  <Product Id="3DA6DF03-E5CD-4A93-B06F-707484742BAB" Name="$(var.ProductDisplayName)" Language="1033" Version="1.48.15.0" Manufacturer="Cainteoir Technologies" UpgradeCode="B4F779EB-AC6C-49D2-A12D-4871E4520C0F">
     <Package InstallerVersion="200" Compressed="yes" InstallScope="perMachine" Platform="$(var.Platform)" />
 
     <MajorUpgrade DowngradeErrorMessage="A newer version of [ProductName] is already installed." />