cpanfile: xref_mapping now requires Text::CSV, recommends Text::CSV_XS
cpanfile: xref_mapping now requires Text::CSV, recommends Text::CSV_XS

Might bump the latter to required at some point but given it is a native
module, let us be careful.

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