Show explorer thumbnails in the search page

[ikesau]

Proposal

The search page currently uses the explorer-views and charts indices. Because they're subsets, we could update the code to use explorer-views-and-charts index and then remove the subset indices.

The reason explorer views are rendered in cards on the search page is because we weren't able to render explorer thumbnails until recently - so we should update the design of the search page by removing the explorer view cards.

Context

In #4031 / #4100, I created a new Algolia search index that merged our explorer-views and charts indices, so that we could precisely control the ranking of these two record types with Algolia's controls (as opposed to querying both indices and merging the results in the client)

This means we are now almost doubling our amount of indexing operations per week:

1. pages (~7500 records)
2. explorers (~100 records)
3. explorer-views (~9000 records)
4. charts (~4500 records)
5. explorer-views-and-charts (~12000 records)

This means we need ~33,000 indexing operations per week.

We will still be comfortably under the Algolia Open Source 200K plan for now, but we only have space for ~8000 new explorer views or charts, before we'll hit the limit (or fewer, depending on how/when we index MDIMs)