Clean up phy_init_nr_gNB()

- variable is_secondary_gnb is not used anywhere, so remove
- variable lowmem is not used/defines should be changed, so remove

executables/nr-gnb.c

@@ -546,7 +546,7 @@ void init_eNB_afterRU(void) {
     gNB = RC.gNB[inst];
     gNB->ldpc_offload_flag = ldpc_offload_flag;
 
-    phy_init_nr_gNB(gNB,0,0);
+    phy_init_nr_gNB(gNB);
 
     // map antennas and PRACH signals to gNB RX
     if (0) AssertFatal(gNB->num_RU>0,"Number of RU attached to gNB %d is zero\n",gNB->Mod_id);