batman-adv: Remove dangling declaration of hash_remove_element

/* allocates and clears the hash */

struct hashtable_t *hash_new(int size);

/* remove element if you already found the element you want to delete and don't

 * need the overhead to find it again with hash_remove().  But usually, you

 * don't want to use this function, as it fiddles with hash-internals. */

void *hash_remove_element(struct hashtable_t *hash, struct element_t *elem);

/* free only the hashtable and the hash itself. */

void hash_destroy(struct hashtable_t *hash);