chassis: 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: I96e8908f07d27696aaf2e2ba33f49411b8e51ec5
Signed-off-by: Gunnar Mills <gmills@us.ibm.com>