ntb: intel: remove b2b memory window workaround for Skylake NTB

The workaround code is never used because Skylake NTB does not need it.

Reported-by: Allen Hubbe <allen.hubbe@dell.com>
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Jon Mason <jdmason@kudzu.us>