libstb/tss: Remove old tss implementation

This is being removed in favor of using a standard TSS library which
offers a more broad implementation that is required for the new
necessities of trusted and secure boot.

Signed-off-by: Mauro S. M. Rodrigues <maurosr@linux.vnet.ibm.com>
Signed-off-by: Oliver O'Halloran <oohall@gmail.com>

Author: maurorodrigues