Exclude 454 single-end data from download_sra_metadata.py results

[mpoelchau]

The pipeline has problems processing data from any 454 instrument (e.g. 454 GS FLX, 454 GS Junior, 454 GS FLX Titanium, but could also be more) that have a single-end layout. Similar to #46, we need to exclude this data type from the download_sra_metadata.py results.

Example error: FileNotFoundError: [Errno 2] No such file or directory: '/project/nal_genomics/shelly.chiang/rnaseq_Hyaazt/2021-06-15-11-54-01/SRR687323/SRR687323_2_fastqc.zip'

Libraries that have this error:

• https://www.ncbi.nlm.nih.gov/sra/SRR687323
• https://www.ncbi.nlm.nih.gov/sra/SRR941560
• https://www.ncbi.nlm.nih.gov/sra/SRR3048546

[mpoelchau]

This is fixed via #49. Closing.