- 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