Remove some dead code

(As suggested by @tilgovi [here](https://github.com/hypothesis/h/commit/c6c6c4e11e0e7492cd1bc80504230346eae023f1).)

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.