Since
21853626ea (built-in rebase: call `git am` directly, 2019-01-18),
the built-in rebase already uses the built-in `git am` directly.
Now that
d03ebd411c (rebase: remove the rebase.useBuiltin setting,
2019-03-18) even removed the scripted rebase, there is no longer any
user of `git-rebase--am.sh`, so let's just remove it.
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>