Tidy up code which supports Elasticsearch 0.9

[MatMoore]

From https://trello.com/c/ZP62CZ7g/8-tidy-up-code-which-supports-elasticsearch-09

Rummager has some code which is backwards-compatible with Elasticsearch 0.9, with the comment:

# Convert to array for consistency between elasticsearch 0.90 and 1.0.
# When we no longer support elasticsearch <1.0, values here will
# always be an array, so this block can be removed.

We are currently using Elasticsearch 2.4, so this can be deleted.