spamassassin: use /etc/mail/spamassassin for config

Using a custom path in the Nix store meant that users of the module
couldn't add their own config files, which is a desirable feature.  I
don't think avoiding /etc buys us anything.

pkgs/servers/mail/spamassassin/default.nix

@@ -9,9 +9,6 @@ perlPackages.buildPerlPackage rec {
     sha256 = "1380cmrgjsyidnznr844c5yr9snz36dw7xchdfryi2s61vjzvf55";
   };
 
-  # https://bz.apache.org/SpamAssassin/show_bug.cgi?id=7434
-  patches = [ ./sa-update_add--siteconfigpath.patch ];
-
   buildInputs = [ makeWrapper ] ++ (with perlPackages; [
     HTMLParser NetCIDRLite NetDNS NetAddrIP DBFile HTTPDate MailDKIM LWP
     IOSocketSSL DBI EncodeDetect IPCountry NetIdent Razor2ClientAgent MailSPF
@@ -22,7 +19,7 @@ perlPackages.buildPerlPackage rec {
   # for the PERL5LIB environment variable. Needs further investigation.
   makeFlags = [ "PERL_BIN=${perlPackages.perl}/bin/perl" "PERL_TAINT=no" ];
 
-  makeMakerFlags = [ "CONFDIR=/homeless/shelter" "LOCALSTATEDIR=/var/lib/spamassassin" ];
+  makeMakerFlags = [ "SYSCONFDIR=/etc LOCALSTATEDIR=/var/lib/spamassassin" ];
 
   doCheck = false;