bs_publish calls publishedhook with array of all changed elements: arg list too long

[bugfinder]

as reported by coolo:

Just spotted in the publisher.log:

running rsync to rsync://download.publish.opensuse.org/put-repos-main at Mon Feb 11 15:24:53 2019
running trigger rsync to rsync://download.publish.opensuse.org/trigger-repos-sync at Mon Feb 11

18:50:39 2019
calling published hook /srv/obs/kiwi/prgs/Backports_upload.sh
Can't exec "/srv/obs/kiwi/prgs/Backports_upload.sh": Argument list too long at
/usr/lib/obs/server/bs_publish line 131.
/srv/obs/kiwi/prgs/Backports_upload.sh: Argument list too long
publish failed for openSUSE:Backports:SLE-15-SP1/standard :
/srv/obs/kiwi/prgs/Backports_upload.sh failed: 256
syncing database (110322 ops)

passing @changed in
qsystem(@$hook, $prp, $extrep, @changed) && die(" @$hook failed: $?\n");
is probably a bad idea as repos can be pretty large ...

[mlschroe]

That @Changed passing needs to be ripped out anyway!