statichttprepo: move HTTPRangeHandler from byterange and delete the latter
It turns out we've been toting around 472 lines of Python just for
this 20-ish line class that teaches urllib how to handle '206 Partial
Content'. byterange.py showed up in my \sstr\( Python 3 dragnet, and
found itself having overstayed its welcome in our codebase.
# no-check-commit because we're moving code that has to have foo_bar naming.
Differential Revision: https://phab.mercurial-scm.org/D2443
ERROR: FIXME: This is a known failure of filelog.size for data starting with \1\n
OK.