Remove incompatible test

Author: jedisct1

test/default/core_ed25519.c

@@ -147,7 +147,6 @@ main(void)
     assert(crypto_core_ed25519_is_valid_point(max_canonical_p) == 1);
     assert(crypto_core_ed25519_is_valid_point(non_canonical_invalid_p) == 0);
     assert(crypto_core_ed25519_is_valid_point(non_canonical_p) == 0);
-    assert(crypto_core_ed25519_is_valid_point(not_main_subgroup_p) == 0);
 
     memcpy(p2, p, crypto_core_ed25519_BYTES);
     add_P(p2);