[ENSCORESW-757]. Cannot perform a fast query on two OR fields from the same table.

Our lookups of primary accessions and display labels with the Xref table was
flawed. Seems MySQL can only use 1 index per query and it is not possible to
create a single index that can handle querying on two columns when either
could be our matching value. Solution is to break the query into two parts
each targetting a single column. MySQL is a lot happier about this and
query times have dropped from 30 seconds on USEast to 18ms (9ms per query).