V4L/DVB (10780): mxl5007t: remove function mxl5007t_check_rf_input_power

This function does not work properly and is not necessary - remove it for now.

Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>