delete_old_mam_messages_batch crashes when using a postgres database

[julien-picalausa]

ejabberd/src/mod_mam_sql.erl

Line 235 in 27b87d4

" where timestamp < %(TS)d and %(ServerHost)H limit %(Batch)d"))

ejabberd/src/mod_mam_sql.erl

Line 258 in 27b87d4

" and %(ServerHost)H limit %(Batch)d"))

Postgresql doesn't support LIMIT in DELETE queries. See https://www.postgresql.org/docs/current/sql-delete.html