iwlwifi: move iwl_dump_nic_error_log to iwlcore module

This patch moves the function iwl_dump_nic_error_log to iwlcore.
Remove sysfs entry it cannot be really triggered.

Signed-off-by: Ester Kummer <ester.kummer@intel.com>
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>