[ref_model] Remove Shape Ops

This removes all code related to following operators:
  DIM
  CONCAT_SHAPE
  ADD_SHAPE
  SUB_SHAPE
  MUL_SHAPE
  DIV_SHAPE

Signed-off-by: Tai Ly <tai.ly@arm.com>
Change-Id: I72bca160280005b0e8b699b78fe9b78cae68b265