Disable 15-test_ecparam.t when configured no-ec2m

This test doesn't actually fail completely, but there's no real
pattern to distinguish which data files should be omitted when no-ec2m
is configured and which should not.

Reviewed-by: Andy Polyakov <appro@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/3103)