Move DLSCH/PDSCH variables to gNB

The next commit will remove msgDataTx. We can therefore not use
msgDataTx to retain the PDSCH/DLSCH variables, and move them to the gNB.

Note that the only reason for NR_gNB_DLSCH_t after this commit is to
hold various large buffers (c, b, f). Future work could be done to
remove this, in which case the array inside PHY_VARS_gNB could be
deleted.

On this occasion, clean up the use of init_DLSCH_struct() and
reset_DLSCH_struct() (renamed destroy_DLSCH_struct()) and centralize
their call in phy_init_nr_gNB()/phy_free_nr_gNB(), and correct
simulators accordingly.

executables/nr-gnb.c

@@ -361,7 +361,6 @@ void init_gNB_Tpool(int inst)
   notifiedFIFO_elt_t *msgL1Tx = newNotifiedFIFO_elt(sizeof(processingData_L1tx_t), 0, &gNB->L1_tx_out, NULL);
   processingData_L1tx_t *msgDataTx = (processingData_L1tx_t *)NotifiedFifoData(msgL1Tx);
   memset(msgDataTx, 0, sizeof(processingData_L1tx_t));
-  init_DLSCH_struct(gNB, msgDataTx);
   // this will be removed when the msgDataTx is not necessary anymore
   gNB->msgDataTx = msgDataTx;