Make TermClose event return the associated buffer

<abuf> from the TermClose event now returns the correct buffer number.

Prior to this change it would always return the buffer number of the current
buffer, which is obviously wrong in an async environment.

src/nvim/eval.c

@@ -22199,7 +22199,6 @@ static void on_process_exit(Process *proc, int status, void *d)
     char msg[22];
     snprintf(msg, sizeof msg, "\r\n[Process exited %d]", proc->status);
     terminal_close(data->term, msg);
-    apply_autocmds(EVENT_TERMCLOSE, NULL, NULL, false, curbuf);
   }
 
   if (data->status_ptr) {