Earlier, on some versions of PDF.js, we used to
use the PDF.js's FindController as a data source
for the text extraction.

However, at some point, we stopped using the
routines shipped with it, since it didn't always
provide use adequate spacing between the various
pieces of texts. So we ended up just contenating
the various pieces of text ourselves.

Then, for new versions of PDF.js, we introduced
other means of accessing the same information,
completely bypassing the PDFFindController.

This change simply unifies the access; now we can
do the same an all PDF.js versions.