staging: pi433: remove unused rf69_set_dc_cut_off_frequency* functions

The following functions:
* rf69_set_dc_cut_off_frequency,
* rf69_set_dc_cut_off_frequency_intern,
* rf69_set_dc_cut_off_frequency_during_afc
are unused and should be removed along with type enum dcc_percent which
was used only by these functions.

Signed-off-by: Marcin Ciupak <marcin.s.ciupak@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>