iwlwifi: drop PCIe workaround applicable for development boards

This patch remove w/a used for development boards.
These boards are not available thus no need to keep it inside driver

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>