iwlwifi: remove uneeded declarations

This patch cleans up iwlwifi by removing uneeded declarations and removing
uneeded symbol export reducing the namespace pollution. It also fixes some
typos in comments.

Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Zhu Yi <yi.zhu@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>