*-login: Removed enforcing maximum calculated fd limit.

Just use the regular ulimit. Login process has become complicated enough
that counting the exact fd size isn't so easy anymore.

Also apparently this low fd limit is causing errors with new Linux kernels:
pop3-login: Error: fd_send(pop3, 18) failed: Too many references: cannot splice

src/login-common/main.c

@@ -346,11 +346,14 @@ static void main_preinit(void)
 	    - 1 for login proxy
 	    - 2 for client-side ssl proxy
 	    - 2 for server-side ssl proxy (with login proxy)
+
+	   However, login process nowadays supports plugins, there are rawlogs
+	   and so on. Don't enforce the fd limit anymore, but use this value
+	   for optimizing the ioloop's fd table size.
 	*/
 	max_fds = MASTER_LISTEN_FD_FIRST + 16 +
 		master_service_get_socket_count(master_service) +
 		master_service_get_client_limit(master_service)*6;
-	restrict_fd_limit(max_fds);
 	io_loop_set_max_fd_count(current_ioloop, max_fds);
 
 	i_assert(strcmp(global_ssl_settings->ssl, "no") == 0 ||