Update proftpd.conf remove IdentLookups directive so install works on recent debian (#3769)

mod_ident removed - see http://www.proftpd.org/docs/RELEASE_NOTES-1.3.7a

install/deb/proftpd/proftpd.conf

@@ -26,7 +26,6 @@ PassivePorts                    12000 12100
 
 <Global>
   Umask                         002
-  IdentLookups                  off
   AllowOverwrite                yes
   <Limit ALL SITE_CHMOD>
     AllowAll