Stop checking for the `response` property, on `XMLHttpRequest`, when setting up the `WorkerMessageHandler`
Stop checking for the `response` property, on `XMLHttpRequest`, when setting up the `WorkerMessageHandler`

This check was added in PR 2445, however it's no longer necessary since all data[1] is now loaded on the main-thread (and then transferred to the worker-thread).
Furthermore, by default the Fetch API is now (usually) used rather than `XMLHttpRequest`.

All in all, while these checks *were* necessary at one point that's no longer the case and they can thus be removed.

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[1] This includes both the actual PDF data, as well as the CMap data.

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