Auto merge of #14527 - servo:xhr-doc, r=Manishearth
Auto merge of #14527 - servo:xhr-doc, r=Manishearth

Remove some redundant code around XMLHttpRequest::document_response().

<!-- Reviewable:start -->
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/14527)
<!-- Reviewable:end -->

splav/servo,splav/servo,emilio/servo,emilio/servo,upsuper/servo,notriddle/servo,KiChjang/servo,paulrouget/servo,saneyuki/servo,SimonSapin/servo,nnethercote/servo,KiChjang/servo,jimberlage/servo,ConnorGBrewster/servo,upsuper/servo,pyfisch/servo,sadmansk/servo,notriddle/servo,dsandeephegde/servo,DominoTree/servo,anthgur/servo,mattnenterprise/servo,jimberlage/servo,cbrewster/servo,eddyb/servo,jimberlage/servo,szeged/servo,dsandeephegde/servo,KiChjang/servo,mbrubeck/servo,szeged/servo,emilio/servo,sadmansk/servo,eddyb/servo,KiChjang/servo,rnestler/servo,mattnenterprise/servo,larsbergstrom/servo,DominoTree/servo,rnestler/servo,peterjoel/servo,pyfisch/servo,saneyuki/servo,canaltinova/servo,fiji-flo/servo,fiji-flo/servo,SimonSapin/servo,splav/servo,DominoTree/servo,dati91/servo,anthgur/servo,upsuper/servo,rnestler/servo,larsbergstrom/servo,upsuper/servo,SimonSapin/servo,rnestler/servo,dati91/servo,pyfisch/servo,cbrewster/servo,splav/servo,peterjoel/servo,pyfisch/servo,larsbergstrom/servo,avadacatavra/servo,emilio/servo,DominoTree/servo,mattnenterprise/servo,CJ8664/servo,larsbergstrom/servo,upsuper/servo,anthgur/servo,DominoTree/servo,emilio/servo,jimberlage/servo,dsandeephegde/servo,notriddle/servo,avadacatavra/servo,anthgur/servo,larsbergstrom/servo,nnethercote/servo,nnethercote/servo,szeged/servo,szeged/servo,ConnorGBrewster/servo,thiagopnts/servo,nnethercote/servo,DominoTree/servo,emilio/servo,DominoTree/servo,eddyb/servo,dati91/servo,splav/servo,avadacatavra/servo,CJ8664/servo,canaltinova/servo,notriddle/servo,larsbergstrom/servo,paulrouget/servo,pyfisch/servo,mattnenterprise/servo,cbrewster/servo,canaltinova/servo,dati91/servo,fiji-flo/servo,DominoTree/servo,larsbergstrom/servo,SimonSapin/servo,thiagopnts/servo,szeged/servo,szeged/servo,szeged/servo,KiChjang/servo,KiChjang/servo,saneyuki/servo,mattnenterprise/servo,saneyuki/servo,avadacatavra/servo,peterjoel/servo,rnestler/servo,ConnorGBrewster/servo,paulrouget/servo,KiChjang/servo,eddyb/servo,paulrouget/servo,thiagopnts/servo,DominoTree/servo,cbrewster/servo,mbrubeck/servo,canaltinova/servo,jimberlage/servo,paulrouget/servo,szeged/servo,avadacatavra/servo,peterjoel/servo,fiji-flo/servo,SimonSapin/servo,peterjoel/servo,paulrouget/servo,fiji-flo/servo,fiji-flo/servo,avadacatavra/servo,notriddle/servo,peterjoel/servo,ConnorGBrewster/servo,cbrewster/servo,mbrubeck/servo,szeged/servo,cbrewster/servo,saneyuki/servo,notriddle/servo,peterjoel/servo,nnethercote/servo,dsandeephegde/servo,dsandeephegde/servo,thiagopnts/servo,dati91/servo,ConnorGBrewster/servo,upsuper/servo,DominoTree/servo,sadmansk/servo,jimberlage/servo,sadmansk/servo,ConnorGBrewster/servo,KiChjang/servo,pyfisch/servo,anthgur/servo,eddyb/servo,splav/servo,thiagopnts/servo,upsuper/servo,fiji-flo/servo,CJ8664/servo,dsandeephegde/servo,emilio/servo,upsuper/servo,jimberlage/servo,emilio/servo,rnestler/servo,thiagopnts/servo,saneyuki/servo,avadacatavra/servo,mbrubeck/servo,cbrewster/servo,dati91/servo,eddyb/servo,paulrouget/servo,sadmansk/servo,splav/servo,CJ8664/servo,saneyuki/servo,nnethercote/servo,larsbergstrom/servo,pyfisch/servo,avadacatavra/servo,dati91/servo,jimberlage/servo,splav/servo,notriddle/servo,emilio/servo,saneyuki/servo,SimonSapin/servo,mattnenterprise/servo,canaltinova/servo,eddyb/servo,dati91/servo,sadmansk/servo,canaltinova/servo,jimberlage/servo,pyfisch/servo,ConnorGBrewster/servo,nnethercote/servo,nnethercote/servo,mbrubeck/servo,splav/servo,mattnenterprise/servo,saneyuki/servo,CJ8664/servo,dsandeephegde/servo,anthgur/servo,emilio/servo,eddyb/servo,thiagopnts/servo,SimonSapin/servo,saneyuki/servo,paulrouget/servo,CJ8664/servo,thiagopnts/servo,anthgur/servo,ConnorGBrewster/servo,CJ8664/servo,SimonSapin/servo,KiChjang/servo,anthgur/servo,peterjoel/servo,mbrubeck/servo,rnestler/servo,canaltinova/servo,KiChjang/servo,nnethercote/servo,mbrubeck/servo,mbrubeck/servo,nnethercote/servo,larsbergstrom/servo,notriddle/servo,CJ8664/servo,paulrouget/servo,splav/servo,dsandeephegde/servo,pyfisch/servo,canaltinova/servo,sadmansk/servo,notriddle/servo,sadmansk/servo,larsbergstrom/servo,peterjoel/servo,peterjoel/servo,pyfisch/servo,rnestler/servo,cbrewster/servo,notriddle/servo,fiji-flo/servo,szeged/servo,paulrouget/servo,mattnenterprise/servo