Remove some dead code

These functions are not used in Annotator standalone mode
or upstream annotator; they were only added for the sake
of H. Since H stopped using them now, there is no reason
to keep them around anymore.
Merge pull request #87 from hypothesis/remove-dead-code

Remove some dead code
Put shortlinks into the document metadata
Merge pull request #93 from hypothesis/shortlink-support-to-document-plugin

Put shortlinks into the document metadata
PDF: add utilities for PDF.js version-based decisions
PDF plugin: user marker classes depending on PDF.js version

See the inline comments in the code.