tests/test-gendoc-el.t

revlog: simplify entry update logic in `rewrite_sidedata`

We don't need to rebuild the full entry. So lets just gather the data we need
to pass to `replace_sidedata_info`.

Differential Revision: https://phab.mercurial-scm.org/D10642

#require docutils gettext

  $ $TESTDIR/check-gendoc el
  checking for parse errors