protocol: Remove extra stdin stream checks
protocol: Remove extra stdin stream checks

The core protocol handling code takes care of validating the frame
fields before calling the stdin handler. We don't need to check them
again.

Signed-off-by: Damien Lespiau <64bd3cb94f359c1a3ce68dae5e26b40578526277@intel.com>

clearcontainers/proxy,clearcontainers/proxy