void remove_friends(const char *name, User **ptr_users) {
    User *curr = *ptr_users;
    while (curr != NULL) {
        for (int i = 0; i < MAX_FRIENDS; i++) {
            if (strcmp(curr->friends[i]->name, name) == 0) {
                for (int j = i; i < MAX_FRIENDS - 1; j ++) {
                    curr->friends[j] = curr->friends[j + 1];
                }
                curr->friends[MAX_FRIENDS - 1] = NULL;
            }
        }
        curr = curr->next;
    }

}
delete the user in every friendlist