PPDs generated after ./configure, make, make dist per HP instructions are the same as the ones we were hosting earlier.

Enabling the class driver results in image failure.  Looks like a precompiled so is being included.  go/fzlyb

hpcups class driver support works without the so files.  Fixing ebuild to only install the filters.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/caa56b14d945687957e917c4079805029bdf228b

commit caa56b14d945687957e917c4079805029bdf228b
Author: Sean Kau <skau@chromium.org>
Date: Thu Nov 15 10:18:26 2018

net-print/hplip: Enable class driver

Configure hpcups to use class PPDs.  Ensure that only the hpcups
and hpps filters are installed as that is all we need.

BUG=chromium:902142
TEST=Verify we can use class PPDs with the installed hpcups filter by printing to an HP ENVY 4520.

Change-Id: I8de2e246b14887b98d82d6fa2bb04f88afe500dd
Reviewed-on: https://chromium-review.googlesource.com/1319030
Commit-Ready: Sean Kau <skau@chromium.org>
Tested-by: Sean Kau <skau@chromium.org>
Reviewed-by: David Valleau <valleau@chromium.org>

[rename] https://crrev.com/caa56b14d945687957e917c4079805029bdf228b/net-print/hplip/hplip-3.18.6-r2.ebuild
[modify] https://crrev.com/caa56b14d945687957e917c4079805029bdf228b/net-print/hplip/hplip-3.18.6.ebuild

The filter update is landed in the image.  We can add the PPDs back with an M72 milestone restriction.

The Class3 PPDs are still broken.  Looks like we imported the Class1 PPDs a while ago.

HP has said there might be a fix in the January update.  We'll need to check against 3.18.13.