remove custom pdfpcnotes package

Phillip Raffeckrequested to merge
pdfpc into master

By now, pdfp provides an upstream latex package which allows the creation of notes. As pdfpc changed the pdfpc-file format to JSON in version 4.5, the custom pacakge is outdated anyways.

For backwards compatibility, the \pnote command is kept as an alias for \pdfpcnote from the pdfpc package.

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