Sensors: Remove odata.context

Redfish made odata.context optional (1.6.0 of DSP0266, Sept 2018).
Redfish 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.

The reason for making optional and removing from mockups/examples,
"no one could figure out how to use it and it did not add value".

Don't see value in it for our implementation.

Change-Id: I8d1c91460ea5836cb793ba1a2774a97649da208a
Signed-off-by: Gunnar Mills <gmills@us.ibm.com>