Remove $registry_register{_TYPE}
Remove $registry_register{_TYPE}

as it does not seem to be used anywhere. Furthermore, the same information
can be derived from $registry_register{_SPECIES}.

This piece of duplicated information take up a lot of spaces for a registry
with large number of species (e.g. ~600MB for Ensembl Bacteria at ~44k species).

Ensembl/ensembl,james-monkeyshines/ensembl,Ensembl/ensembl,muffato/ensembl,Ensembl/ensembl,muffato/ensembl,james-monkeyshines/ensembl,james-monkeyshines/ensembl,james-monkeyshines/ensembl,muffato/ensembl,Ensembl/ensembl,muffato/ensembl