Update to Ensembl release 74.

Also remove the unnecessary FASTA file that is generated from
the final tarball.
Update to latest releases of RNA-seq data with Ensembl 74 annotations
Update to latest releases of RNA-seq data with Ensembl 74 annotations
Add featureCounts.

This will replace htseq-count; it has similar functionality and
is about 10x faster.
Do full cleanup of outdated brew package prior to reinstall. Avoids unexpected state errors when upgrading.