Instant Search: Improve JSX handling with Preact

We currently use [a global JSX pragma](https://preactjs.com/guide/v8/getting-started/#global-pragma) `/** @jsx h */` in every component file to tell Babel to transform JSX into
`Preact.h( ... )`.

Ideally, we would no longer need to insert this pragma nor `import { h } from 'preact'` in the future.

The issue names no specific files or tests. Start by locating the Instant Search component files and their Babel JSX configuration, then verify that JSX still transforms correctly without the global pragma or the Preact h import; done means the boilerplate is no longer required.

Written by the indexing model from the issue text.