Remove unneeded generate_ed_link_cert() in tests.

This fixes CID 1465291, which was a complaint that we never actually
checked the return value of this function.  It turns out that this
function was failing, and it didn't matter, because it wasn't
necessary for this test.

src/test/test_routerkeys.c

@@ -111,7 +111,6 @@ test_routerkeys_write_ed25519_identity(void *arg)
   set_client_identity_key(crypto_pk_dup_key(key));
 
   load_ed_keys(options, now);
-  generate_ed_link_cert(options, now, 0);
   tt_assert(get_master_identity_key());
 
   tt_int_op(0, OP_EQ, check_private_dir(ddir, CPD_CREATE, NULL));