The XS was left only for the unit / integration tests, and it links libslic3r only. No wxWidgets are allowed to be used from Perl starting from now.
on some Perl/XS installations (strawberry Perl 64bit)
Having the expat parser inside the Slic3r source base makes life easier on non-Linux systems and it also allows us to configure the Expat parser for maximum performance by disabling all unneeded features.