Clean up program name handling in oenv

Clean up program name handling in oenv

- Remove unused functions to access the program name and command line
  from oenv.
- Replace these with direct access to a ProgramContextInterface, and use
  that instead of the global program context instance in places where
  output_env_t is easily accessible.
- Replace some calls to ShortProgram() with an equivalent call in oenv
  for places where oenv is readily accessible.

Change-Id: I2e8bc8701b8217f51ed9936338e1e9c3c21bd8ba