miRBase old versions are no longer available

[rchekaluk]

Reviewing mirbase.org shows that the URLs for downloading have changed (see CURRENT/genomes), but old versions are not available.

Only version 22.1 is available at PREVIOUS_RELEASES , so there is no obvious place to download these from:

./ggd-recipes/mm10/mirbase.yaml:        wget  --random-wait --retry-connrefused -q -N -c https://www.mirbase.org/ftp/20/genomes/mmu.gff3
./ggd-recipes/rn6/mirbase.yaml:        # wget -q -N -c ftp://mirbase.org/pub/mirbase/20/genomes/rno.gff3
./ggd-recipes/hg19/mirbase.yaml:        wget --random-wait --retry-connrefused -nv -c -O hsahg19.gff3 https://www.mirbase.org/ftp/20/genomes/hsa.gff3
./ggd-recipes/GRCh37/mirbase.yaml:        wget --random-wait --retry-connrefused -nv -c -O hsahg19.gff3 https://www.mirbase.org/ftp/20/genomes/hsa.gff3

Supercedes #3720