cryptodev: fix build with icc

cryptodev: fix build with icc

Removed unnecessary macro RTE_STD_C11, which is used
for unnamed structs.
Since there is no longer an unnamed structure in
rte_cryptodev_sym_session, this is not needed and
it is actually breaking compilation on icc:

lib/librte_cryptodev/rte_cryptodev.h(887): error: expected a declaration
  	__extension__ void *sess_private_data[0];
  	^
Fixes: 7c110ce7aa4e ("cryptodev: remove mempool from session")

Signed-off-by: Pablo de Lara <pablo.de.lara.guarch@intel.com>
Acked-by: Declan Doherty <declan.doherty@intel.com>