on REFER from fs, remove incoming Contact header before sending onward

lib/call-session.js

@@ -999,7 +999,7 @@ Duration=${payload.duration} `
           // eslint-disable-next-line no-unused-vars
           'content-length':contentlength, 'refer-to':_referto, 'referred-by':_referredby,
           // eslint-disable-next-line no-unused-vars
-          'X-Refer-To-Leave-Untouched': _leave,
+          'X-Refer-To-Leave-Untouched': _leave, 'contact':_contact,
           ...customHeaders
         } = req.headers;