There was concern that someone in the future might call the function
with the wrong inputs. So, based on the discussion on the MR below
https://gitlab.eurecom.fr/oai/openairinterface5g/-/merge_requests/2916#note_132506
the SIMD for multiplying DMRS vector with amplitude is removed and is
now done with plain C (no SIMD).

The execution time for the function dmrs_amp_mult() in this commit is
10x higher that the previous commit.