ethernet: Remove odata.context

Redfish made odata.context optional (1.6.0 of DSP0266),
has removed odata.context from example payloads in the
specification (1.7.0 of DSP0266), removed it from the mockups,
and Redfish recommended not using.

Change-Id: I5a78856c510f063df67999bb8196e77401c56aac
Signed-off-by: Gunnar Mills <gmills@us.ibm.com>