manager: Remove odata.context

Redfish made odata.context optional (1.6.0 of DSP0266) and
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: I1a229e996b30b4223036c58a111e4c3ab4b749c6
Signed-off-by: Gunnar Mills <gmills@us.ibm.com>