iwlegacy: remove several redundant variables

Variables id, unicast, write, conf, a_band, accum_tx and ucode are
assigned a value but it is never read, hence they are redundant and
can be removed.

Cleans up clang warnings:
warning: variable 'id' set but not used [-Wunused-but-set-variable]
warning: variable 'unicast' set but not used [-Wunused-but-set-variable]
warning: variable 'write' set but not used [-Wunused-but-set-variable]
warning: variable 'conf' set but not used [-Wunused-but-set-variable]
warning: variable 'a_band' set but not used [-Wunused-but-set-variable]
warning: variable 'tx' set but not used [-Wunused-but-set-variable]
warning: variable 'accum_tx' set but not used [-Wunused-but-set-variable]
warning: variable 'ucode' set but not used [-Wunused-but-set-variable]

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Stanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>