Remove some dormant code from nxt_process_quit().

In nxt_process_quit() there is a loop that iterates over the
task->thread->runtime->listen_sockets array and closes the connections.

This code has been there from the beginning

  $ git log --pretty=oneline -S'if (rt->listen_sockets != NULL)'
  e9e5ddd5a5 Refactor of process management.
  6f2c9acd18 Processes refactoring. The cycle has been renamed to the runtime.
  $ git log --pretty=oneline -S'if (cycle->listen_sockets != NULL) {'
  6f2c9acd18 Processes refactoring. The cycle has been renamed to the runtime.
  16cbf3c076 Initial version.

but never seems to have been used (AFAICT and certainly not recently,
confirmed by code inspection and running pytests with a bunch of
language modules enabled and the code in question was never executed) as
the listen_sockets array has never been populated... until now.

The previous commit now adds Unix domain sockets to this array so that
they can be unlink(2)'d upon exit and reconfiguration.

This has now caused this dormant code to become active as it now tries
to close these sockets (from at least the prototype processes), this
array is inherited via fork by other processes.

The file descriptor for these sockets is set to -1 when they are put
into this array. This then results in close(-1) calls which caused
multiple failures in the pytests such as

  >       assert not alerts, 'alert(s)'
  E       AssertionError: alert(s)
  E       assert not ['2023/03/09 23:26:14 [alert] 137673#137673 socket close(-1) failed (9: Bad file descriptor)']

I think the simplest thing is to just remove this code.

Reviewed-by: Alejandro Colomar <alx@nginx.com>
Signed-off-by: Andrew Clayton <a.clayton@nginx.com>

src/nxt_process.c

@@ -1251,14 +1251,9 @@ nxt_process_close_ports(nxt_task_t *task, nxt_process_t *process)
 void
 nxt_process_quit(nxt_task_t *task, nxt_uint_t exit_status)
 {
-    nxt_uint_t           n;
     nxt_queue_t          *listen;
-    nxt_runtime_t        *rt;
     nxt_queue_link_t     *link, *next;
     nxt_listen_event_t   *lev;
-    nxt_listen_socket_t  *ls;
-
-    rt = task->thread->runtime;
 
     nxt_debug(task, "close listen connections");
 
@@ -1275,21 +1270,5 @@ nxt_process_quit(nxt_task_t *task, nxt_uint_t exit_status)
         nxt_fd_event_close(task->thread->engine, &lev->socket);
     }
 
-    if (rt->listen_sockets != NULL) {
-
-        ls = rt->listen_sockets->elts;
-        n = rt->listen_sockets->nelts;
-
-        while (n != 0) {
-            nxt_socket_close(task, ls->socket);
-            ls->socket = -1;
-
-            ls++;
-            n--;
-        }
-
-        rt->listen_sockets->nelts = 0;
-    }
-
     nxt_runtime_quit(task, exit_status);
 }