doc: remove driver interface header from API index
doc: remove driver interface header from API index

The file rte_flow_driver.h is a driver interface,
thus it should not be listed in the API index.

Signed-off-by: Thomas Monjalon <5f50a84c1fa3bcff146405017f36aec1a10a9e38@monjalon.net>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk