ethdev: remove deprecated port count function

ethdev: remove deprecated port count function

The function rte_eth_dev_count() was marked as deprecated in DPDK 18.05
in commit d9a42a69febf ("ethdev: deprecate port count function").
It was planned to be removed after 19.11 LTS release,
but given we must not break ABI between 19.11 and 20.11,
it is removed now.

Note the ABI version is not dumped in this commit
because other changes already did.

Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
Reviewed-by: David Marchand <david.marchand@redhat.com>
Reviewed-by: Andrew Rybchenko <arybchenko@solarflare.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Reviewed-by: Jerin Jacob <jerinj@marvell.com>