message: Remove core API forward from tink.
diff: @@ -39,11 +39,6 @@ Mac = mac.Mac
  PublicKeySign = signature.PublicKeySign
  PublicKeyVerify = signature.PublicKeyVerify
  -KeyManager = core.KeyManager
  -PrivateKeyManager = core.PrivateKeyManager
  -
  -Registry = core.Registry
  -
  new_keyset_handle = _keyset_handle.new_keyset_handle
  read_keyset_handle = _keyset_handle.read_keyset_handle
  read_no_secret_keyset_handle = _keyset_handle.read_no_secret_keyset_handle
  @@ -58,6 +53,4 @@ KeysetWriter = _keyset_writer.KeysetWriter
  JsonKeysetWriter = _keyset_writer.JsonKeysetWriter
  BinaryKeysetWriter = _keyset_writer.BinaryKeysetWriter
  -new_primitive_set = core.new_primitive_set
  -
  TinkError = core.TinkError
  