Remove EC_EXTRA_DATA

Remove EC_EXTRA_DATA

With the ecdh_check() and ecdsa_check() abominations gone, we can finally
get rid of EC_EXTRA_DATA and EC_KEY_{get,insert}_key_method_data(). The
EC_EX_DATA_*() handlers, (which fortunately have always had "'package'
level visibility") join the ride to the great bit bucket in the sky.

Thanks to op for making this possible.

ok jsing