staging: r8188eu: core: remove unused function rtw_set_tx_chksum_offload

Remove unused function rtw_set_tx_chksum_offload.

Signed-off-by: Saurav Girepunje <saurav.girepunje@gmail.com>
Link: https://lore.kernel.org/r/YT4xcJvvlPSIS+T6@user


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>