Switch OpenSSLECDHKeyAgreement to KeyFactory.translateKey.

OpenSSL KeyFactory.translateKey encapsulates all the functionality
for translating arbitrary Key instances to OpenSSL-backed Key
instances. Thus, there's no need to replicate that functionality
elsewhere.

(cherry picked from commit 0469e3a6a9b5e854b8b985039de8ba4f6e6037bd)

Change-Id: I4caa0021e51a83be6932617117275fd033b6d5f7
3 files changed