b43legacy: Remove unused b43legacy_radio_set_tx_iq()

Remove the function b43legacy_radio_set_tx_iq() that is not used anywhere.

This was partially found by using a static code analysis program called cppcheck.

Signed-off-by: Rickard Strandqvist <rickard_strandqvist@spectrumdigital.se>
Acked-by: Larry Finger <Larry.Finger@lwfinger.net>
Acked-by: Rafa? Mi?ecki <zajec5@gmail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>