[476477] Provide a way to run latest installer on systems without GTK

2.18.0

The platform no longer supports GTK 2 so no point in having an
instruction of use that in the installer product file.

https://bugs.eclipse.org/bugs/show_bug.cgi?id=476477

products/org.eclipse.oomph.setup.installer.product/Installer.product

@@ -17,9 +17,6 @@ Eclipse Installer
 -data
 @noDefault
       </programArgs>
-      <programArgsLin>--launcher.GTK_version
-2
-      </programArgsLin>
       <vmArgs>-Xms256M
 -Xmx1024M
       </vmArgs>