Use license in product.json for rpm

Fixes microsoft#17133

linux/rpm/code.spec.template

@@ -5,7 +5,7 @@ Summary:  Code editing. Redefined.
 Group:    Development/Tools
 Vendor:   Microsoft Corporation
 Packager: Visual Studio Code Team <vscode-linux@microsoft.com>
-License:  Multiple, see https://code.visualstudio.com/license
+License:  @@LICENSE@@
 URL:      https://code.visualstudio.com/
 Icon:     @@NAME@@.xpm
 Requires: @@DEPENDENCIES@@