ldb: Free memory when repacking database

ldb: Free memory when repacking database

The msg for each database record is allocated on the module context, but
never freed. The module seems like it could be a long-running context (as
the database would normally get repacked by the samba executable).

Even if it's not a proper leak, it shouldn't hurt to cleanup the memory.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=14059

Signed-off-by: Tim Beale <timbeale@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Garming Sam <garming@catalyst.net.nz>