am aab6d576: Revert "ECIES: add HKDF (specified in RFC 5869) using HMAC-SHA256"

* commit 'aab6d5768e89cc6b1af249ff2e4b9f90e788ef58':
  Revert "ECIES: add HKDF (specified in RFC 5869) using HMAC-SHA256"