nixos/tt-rss: fix and significantly simplify database setup

the schema files referenced in the current preStart are empty.
other ones exist, but don't apply cleanly either.
calling update.php with --update-schema works for initial setup and
updates. if the database schema is already up to date, it's idempotent.

nixos/modules/services/web-apps/tt-rss.nix

@@ -595,47 +595,9 @@ let
       tt-rss = {
         description = "Tiny Tiny RSS feeds update daemon";
 
-        preStart = let
-          callSql = e:
-              if cfg.database.type == "pgsql" then ''
-                  ${optionalString (cfg.database.password != null) "PGPASSWORD=${cfg.database.password}"} \
-                  ${optionalString (cfg.database.passwordFile != null) "PGPASSWORD=$(cat ${cfg.database.passwordFile})"} \
-                  ${config.services.postgresql.package}/bin/psql \
-                    -U ${cfg.database.user} \
-                    ${optionalString (cfg.database.host != null) "-h ${cfg.database.host} --port ${toString dbPort}"} \
-                    -c '${e}' \
-                    ${cfg.database.name}''
-
-              else if cfg.database.type == "mysql" then ''
-                  echo '${e}' | ${config.services.mysql.package}/bin/mysql \
-                    -u ${cfg.database.user} \
-                    ${optionalString (cfg.database.password != null) "-p${cfg.database.password}"} \
-                    ${optionalString (cfg.database.host != null) "-h ${cfg.database.host} -P ${toString dbPort}"} \
-                    ${cfg.database.name}''
-
-              else "";
-
-        in (optionalString (cfg.database.type == "pgsql") ''
-          exists=$(${callSql "select count(*) > 0 from pg_tables where tableowner = user"} \
-          | tail -n+3 | head -n-2 | sed -e 's/[ \n\t]*//')
-
-          if [ "$exists" == 'f' ]; then
-            ${callSql "\\i ${pkgs.tt-rss}/schema/ttrss_schema_${cfg.database.type}.sql"}
-          else
-            echo 'The database contains some data. Leaving it as it is.'
-          fi;
-        '')
-
-        + (optionalString (cfg.database.type == "mysql") ''
-          exists=$(${callSql "select count(*) > 0 from information_schema.tables where table_schema = schema()"} \
-          | tail -n+2 | sed -e 's/[ \n\t]*//')
-
-          if [ "$exists" == '0' ]; then
-            ${callSql "\\. ${pkgs.tt-rss}/schema/ttrss_schema_${cfg.database.type}.sql"}
-          else
-            echo 'The database contains some data. Leaving it as it is.'
-          fi;
-        '');
+        preStart = ''
+          ${pkgs.php81}/bin/php ${cfg.root}/www/update.php --update-schema
+        '';
 
         serviceConfig = {
           User = "${cfg.user}";