iwlwifi: eliminate iwl4965_mac_get_tsf

This patch removes iwl4965_mac_get_tsf, as this function does not
currently reports any actual value.

Signed-off-by: Ron Rindjunsky <ron.rindjunsky@intel.com>
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Zhu Yi <yi.zhu@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>