nixos/freshrss: migrate to DATA_PATH

nixos/modules/services/web-apps/freshrss.nix

···
             "catch_workers_output" = true;
           };
           phpEnv = {
-            FRESHRSS_DATA_PATH = "${cfg.dataDir}";
+            DATA_PATH = "${cfg.dataDir}";
           };
         };
       };
···
             WorkingDirectory = cfg.package;
           };
           environment = {
-            FRESHRSS_DATA_PATH = cfg.dataDir;
+            DATA_PATH = cfg.dataDir;
           };
 
           script =
···
         wantedBy = [ "multi-user.target" ];
         startAt = "*:0/5";
         environment = {
-          FRESHRSS_DATA_PATH = cfg.dataDir;
+          DATA_PATH = cfg.dataDir;
         };
         serviceConfig = defaultServiceConfig //{
           ExecStart = "${cfg.package}/app/actualize_script.php";

pkgs/servers/web-apps/freshrss/default.nix

···
   # There's nothing to build.
   dontBuild = true;
 
-  # the data folder is no in this package and thereby declared by an env-var
-  overrideConfig = pkgs.writeText "constants.local.php" ''
-    <?php
-      define('DATA_PATH', getenv('FRESHRSS_DATA_PATH'));
-  '';
-
   postPatch = ''
     patchShebangs cli/*.php app/actualize_script.php
   '';
···
   installPhase = ''
     mkdir -p $out
     cp -vr * $out/
-
-    cp $overrideConfig $out/constants.local.php
   '';
 
   meta = with lib; {