Note: this won't affect M56 users, because the result of this is that imageloader crashes when trying to delete the old version. But that is after the new version was installed. 

However, there are still some obvious negative effects such as:
1) A crash happening in general
2) The "restart to update" dialog will never show (this isn't present in M56)
3) Old versions will start to build up.

Note that as follow up to this, my main development priority for imageloader is currently to write an autotest to take it through all it's possible flows.

We have an autotest for flash component updates thanks to ihf@, but that only covers the basic/expected flow. With an autotest that uses pre-packaged test data, we can test more interesting cases, such as an update on top of an update.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/platform/imageloader/+/466101c5a52696b50a075cfe767bb22c4df9b181

commit 466101c5a52696b50a075cfe767bb22c4df9b181
Author: Greg Kerr <kerrnel@chromium.org>
Date: Thu Dec 22 01:17:36 2016

Add unlink to the seccomp filter for imageloader.

unlink(2) is necessary for the ImageLoader to delete old versions of
components.

BUG= chromium:676444 
TEST=emerge-${BOARD} imageloader and manually test an update on top of
an existing updates, which forces cleanup

Change-Id: Iae98426964def8bc7d68ea8db8ae8d7b97b4e819
Reviewed-on: https://chromium-review.googlesource.com/422586
Commit-Ready: Greg Kerr <kerrnel@chromium.org>
Tested-by: Greg Kerr <kerrnel@chromium.org>
Reviewed-by: Mattias Nissler <mnissler@chromium.org>

[modify] https://crrev.com/466101c5a52696b50a075cfe767bb22c4df9b181/imageloader-seccomp-amd64.policy
[modify] https://crrev.com/466101c5a52696b50a075cfe767bb22c4df9b181/imageloader-seccomp-arm.policy
[modify] https://crrev.com/466101c5a52696b50a075cfe767bb22c4df9b181/imageloader-seccomp-x86.policy