Clean up X509_to_X509_REQ()

Clean up X509_to_X509_REQ()

Use better variable names. X509_REQ_new() sets the version to the only
specified version, so there is no point to set it. Extract the subject
name, then assign to make it more obvious that we error happens if the
cert has a missing subject. Switch to X509_get0_pubkey() to avoid some
strange dance with a strangely named variable to adjust the refcount.

ok jsing