logind: remove unused session->closing field

This field is always false, drop it. If you want a reliable way to get
session state, call session_get_state(). Testing for any flags directly
doesn't work currently so don't pretend it would.

src/login/logind-dbus.c

@@ -1252,7 +1252,6 @@ static int have_multiple_sessions(
          * count, and non-login sessions do not count either. */
         HASHMAP_FOREACH(session, m->sessions, i)
                 if (session->class == SESSION_USER &&
-                    !session->closing &&
                     session->user->uid != uid)
                         return true;
 

src/login/logind-session.c

@@ -954,9 +954,6 @@ void session_add_to_gc_queue(Session *s) {
 SessionState session_get_state(Session *s) {
         assert(s);
 
-        if (s->closing)
-                return SESSION_CLOSING;
-
         if (s->scope_job)
                 return SESSION_OPENING;
 

src/login/logind-session.h

@@ -107,7 +107,6 @@ struct Session {
 
         bool in_gc_queue:1;
         bool started:1;
-        bool closing:1;
 
         sd_bus_message *create_message;