Remove unnecessary nilling of the cache.
Remove unnecessary nilling of the cache.

In cases involving customisation, we need to keep this around because
we can't currently customise cache sizes and TTLs on individual adapter
instances. I think this is a bug.

bitzesty/gds-api-adapters,theodi/gds-api-adapters,alphagov/gds-api-adapters,theodi/gds-api-adapters,bitzesty/gds-api-adapters