SE data - the cutadapt output file name is needed for scripts

Currently `01_scripts/03_retain_unique.sh` is operating on the 'cut to 230 bp' fastq file, but this needs to be specifically pointed to, as the standard works on `*assi.fq` instead of `*assi_230.fq`. 
Need to find a solution that when cutadapt works, the following script is not needed to fix it.  