Remove unused file from Chromium extension

`extensions/chromium/patch-worker.js` was already redundant since edd4bae903c36048b7d4d4bed393e4408d0198ba (it was only used at https://github.com/mozilla/pdf.js/commit/edd4bae903c36048b7d4d4bed393e4408d0198ba#diff-79d6f62f6441534f1c4eb24782e55eb4L79).