Remove the unused `isWorker` property from `src/display/global.js`
Remove the unused `isWorker` property from `src/display/global.js`

This has been completely unused since commit https://github.com/mozilla/pdf.js/commit/1d12aed5cac6a0caccb0550e0aad4ef9f6bb263d, in PR 7126, almost one and a half years ago.

adlerweb/pdf.js-Touch,macroplant/pdf.js,mainegreen/pdf.js,mainegreen/pdf.js,caremerge/pdf.js,mozilla/pdf.js,mozilla/pdf.js,timvandermeij/pdf.js,Rob--W/pdf.js,Snuffleupagus/pdf.js,macroplant/pdf.js,caremerge/pdf.js,mukulmishra18/pdf.js,Shoobx/pdf.js,nawawi/pdf.js,nawawi/pdf.js,websirnik/pdf.js,xavier114fch/pdf.js,showpad/mozilla-pdf.js,timvandermeij/pdf.js,adlerweb/pdf.js-Touch,nawawi/pdf.js,showpad/mozilla-pdf.js,Snuffleupagus/pdf.js,xavier114fch/pdf.js,Shoobx/pdf.js,Shoobx/pdf.js,mukulmishra18/pdf.js,websirnik/pdf.js,Snuffleupagus/pdf.js,macroplant/pdf.js,timvandermeij/pdf.js,mozilla/pdf.js,showpad/mozilla-pdf.js,Rob--W/pdf.js