Remove rspamd size limit

This ensures that the spam and antivirus filters cannot be evaded by making the message large enough.
Rspamd does not need a size limit on its own (e.g. for DoS protection) as Postfix already has a size limit (message_size_limit).

data/conf/rspamd/local.d/antivirus.conf

@@ -1,6 +1,5 @@
 clamav {
   attachments_only = false;
-  max_size = 20000000;
   symbol = "CLAM_VIRUS";
   type = "clamav";
   log_clean = true;