The global variable rx_gain_off was always 0.0, as it was not even modified by the NR UE command line parameter --ue-rxgain-off.
That command line parameter modified only a parameter in the struct nrUE_params_t, which was not used at all and is removed in this commit, too.
Also, the global variable rx_gain_off was just added to rx_total_gain_dB and subtracted from it again in nr_rf_card_config_gain().
So we simplify that function slightly, too.