net/mlx5e: Remove unused max inline related code

Commit 58d52291 ("net/mlx5e: Support TX packet copy into WQE")
introduced the max inline WQE as an ethtool tunable. One commit later,
that functionality was made dependent on BlueFlame.

Commit 6982ab60

 ("net/mlx5e: Xmit, no write combining") removed
BlueFlame support, and with it the max inline WQE.
This patch cleans up the leftovers from the removed feature.

Signed-off-by: Gal Pressman <galp@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>