Deleting ***SPAM*** messages
Yes you can remove them. You need to get amavis to perform evasive actions on all spam emails. What you need to do is to decide what spam level is the limit, and set both $sa_tag2_level_deflt and $sa_kill_level_deflt variables in amavisd.conf to the same value, e.g.
$sa_tag2_level_deflt = 2.3; # add 'spam detected' headers at that level
$sa_kill_level_deflt = 2.3; # triggers spam evasive actions
Admittedly 2.3 is fairly low - you may want it around 4, but that's up to you.
What will happen here is that the first variable will mark the incoming junk mail as spam, and add the ***SPAM*** header. The second variable will also notice that the junk mail is above the 'Kill All' level and will delete the email for you.