moduhashlib: Remove not implemented .hexdigest().

Effect can be easily achieved by ubinsacii.hexlify(hash.digest()).

extmod/moduhashlib.c

@@ -70,22 +70,9 @@ STATIC mp_obj_t hash_digest(mp_obj_t self_in) {
 }
 MP_DEFINE_CONST_FUN_OBJ_1(hash_digest_obj, hash_digest);
 
-STATIC mp_obj_t hash_hexdigest(mp_obj_t self_in) {
-    (void)self_in;
-    mp_not_implemented("");
-#if 0
-    mp_obj_hash_t *self = self_in;
-    byte hash[SHA256_BLOCK_SIZE];
-    sha256_final((SHA256_CTX*)self->state, hash);
-    return mp_obj_new_str((char*)hash, SHA256_BLOCK_SIZE, false);
-#endif
-}
-MP_DEFINE_CONST_FUN_OBJ_1(hash_hexdigest_obj, hash_hexdigest);
-
 STATIC const mp_map_elem_t hash_locals_dict_table[] = {
     { MP_OBJ_NEW_QSTR(MP_QSTR_update), (mp_obj_t) &hash_update_obj },
     { MP_OBJ_NEW_QSTR(MP_QSTR_digest), (mp_obj_t) &hash_digest_obj },
-    { MP_OBJ_NEW_QSTR(MP_QSTR_hexdigest), (mp_obj_t) &hash_hexdigest_obj },
 };
 
 STATIC MP_DEFINE_CONST_DICT(hash_locals_dict, hash_locals_dict_table);