Moved UE UL scheduling functions to new MAC file

- this commit was necessary because the location of the MAC UE
  functions does not reflect the context in which they are used
- therefore all UL scheduling-related functions have been moved
  to a new nr_ue_scheduler.c file
- and the irrelevant file rar_tools_nrUE.c has been deleted
  (nr_ue_process_rar moved to nr_ue_procedures)
- the new locations are supposed to make the file and functions
  organisations more structured and cleaner

cmake_targets/CMakeLists.txt

@@ -2109,10 +2109,10 @@ set (MAC_NR_SRC_UE
   ${NR_UE_MAC_DIR}/mac_vars.c
   ${NR_UE_MAC_DIR}/main_ue_nr.c
   ${NR_UE_MAC_DIR}/nr_ue_procedures.c
+  ${NR_UE_MAC_DIR}/nr_ue_scheduler.c
   ${NR_UE_MAC_DIR}/nr_ue_dci_configuration.c
   ${NR_UE_MAC_DIR}/nr_l1_helpers.c
   ${NR_UE_MAC_DIR}/nr_ra_procedures.c
-  ${NR_UE_MAC_DIR}/rar_tools_nrUE.c
 )
 
 set (ENB_APP_SRC