Remove the unused "GetIsPureXfa" message handler in the worker (PR 13069 follow-up)
Remove the unused "GetIsPureXfa" message handler in the worker (PR 13069 follow-up)

Looking at the API, there's no code which actually sends this message. Most likely it's a left-over from a previous version of PR 13069, since the `isPureXfa` parameter is being included in the "GetDoc" message.

timvandermeij/pdf.js,Shoobx/pdf.js,Snuffleupagus/pdf.js,showpad/mozilla-pdf.js,xavier114fch/pdf.js,macroplant/pdf.js,showpad/mozilla-pdf.js,nawawi/pdf.js,Shoobx/pdf.js,timvandermeij/pdf.js,macroplant/pdf.js,xavier114fch/pdf.js,Shoobx/pdf.js,timvandermeij/pdf.js,mozilla/pdf.js,showpad/mozilla-pdf.js,macroplant/pdf.js,mozilla/pdf.js,nawawi/pdf.js,Snuffleupagus/pdf.js,nawawi/pdf.js,mozilla/pdf.js,Snuffleupagus/pdf.js