Float code cleanup changes for lib_dec, stere_dft_enc_itd.c

Pipeline results:

• EVS 26.444 BE test passes.
• decoder pytests:
  MLD scores:
  Original inputs: 562 failed, 374 skipped
  MLD > 10: 8
  MLD > 5 : 76
  MLD < 5 : 478
  +10dB inputs: 562 failed, 374 skipped
  MLD > 10: 102
  MLD > 5 : 182
  MLD < 5 : 278
  -10dB inputs: 562 failed, 374 skipped
  MLD > 10: 2
  MLD > 5 : 17
  MLD < 5 : 542
• encoder pytests results:
  MLD scores:
  Original inputs: 562 tests:
  MLD > 10: 18
  MLD > 5 : 71
  MLD < 5 : 473
  +10dB inputs: 562 tests:
  MLD > 10: 66
  MLD > 5 : 124
  MLD < 5 : 372
  -10dB inputs: 562 tests:
  MLD > 10: 5
  MLD > 5 : 30
  MLD < 5 : 527