iwlwifi: remove extra statistics request from debugfs

When reading current ucode statistics information from debugfs, in
current implementation, it will always send a new "statistics request" to
uCode. In normal operation, uCode should report the statistics per beacon
interval. Remove this extra request to reduce the additional command exchanges
between driver and uCode.

Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>