Integrate nr_fill_nfapi_dl_pdu() back into nr_schedule_ue_spec()

Initially, filling the PDCCH and PDSCH nFAPI messages was split into a
separate function (in an attempt to keep the code structure similar to
LTE). However, this proved as not helpful: the nr_fill_nfapi_dl_pdu()
just filled the messages, with a parameter list almost size as long as
the actual messages (because most parameters are kind of independent).
This made no sense, so we put it back.

Also, from an understanding POV, they just fill a message as specified
in SCF222, so it should not be a problem.

openair2/LAYER2/NR_MAC_gNB/mac_proto.h

@@ -170,22 +170,6 @@ void nr_schedule_css_dlsch_phytest(module_id_t   module_idP,
                                    frame_t       frameP,
                                    sub_frame_t   subframeP);
 
-void nr_fill_nfapi_dl_pdu(int Mod_id,
-                          nfapi_nr_dl_tti_request_body_t *dl_req,
-                          rnti_t rnti,
-                          NR_CellGroupConfig_t *secondaryCellGroup,
-                          NR_UE_sched_ctrl_t *sched_ctrl,
-                          NR_sched_pucch_t *pucch_sched,
-                          nfapi_nr_dmrs_type_e dmrsConfigType,
-                          uint16_t R,
-                          uint8_t Qm,
-                          uint32_t tbs,
-                          int StartSymbolIndex,
-                          int NrOfSymbols,
-                          int harq_pid,
-                          int ndi,
-                          int round);
-
 void handle_nr_uci_pucch_0_1(module_id_t mod_id,
                              frame_t frame,
                              sub_frame_t slot,