[Minor] Filter artificial Received header in multimap by default

 - Also filter headers in CHECK_RECEIVED rule

rules/misc.lua

 -- This is main lua config file for rspamd
 
 local E = {}
+local fun = require "fun"
 local util = require "rspamd_util"
 local rspamd_regexp = require "rspamd_regexp"
 
 rspamd_config.CHECK_RECEIVED = {
   callback = function (task)
     local received = task:get_received_headers()
+    received = fun.filter(function(h)
+      return not h['artificial']
+    end, received):totable()
     task:insert_result('RCVD_COUNT_' .. #received, 1.0)
   end
 }
 
 rspamd_config.OMOGRAPH_URL = {
   callback = function(task)
-    local fun = require "fun"
     local urls = task:get_urls()
 
     if urls then

src/plugins/lua/multimap.lua

     received = function()
       local hdrs = task:get_received_headers()
       if hdrs and hdrs[1] then
+        if not rule['artificial'] then
+          hdrs = fun.filter(function(h)
+            return not h['artificial']
+          end, hdrs):totable()
+        end
         for pos, h in ipairs(hdrs) do
           match_received_header(rule, pos, #hdrs, h)
         end