absorb: improve message for the case when changeset became empty
In changeset f55099982bc5, I introduced the message "became empty and became
...", which I was never very happy with. Raphaël Gomès suggested "became empty
as ...". That sounds much nicer.
Differential Revision: https://phab.mercurial-scm.org/D8765
#require docutils gettext
$ $TESTDIR/check-gendoc da
checking for parse errors