In order to package a project as extension , a meta data file called asf.xml is required. By default, studio will auto generate this file when you invoke packaging.This auto generated asf.xml is added as link under the meta data folder vsix as shown below.
It also has the option to use the asf.xml added by the user, in this case user has to disable auto generation of asf.xml file. To disable it Go to Auto generate asf.xml to false as shown below.
and choose XDK settings to set the option