Use `olm-loader` in all crypto tests
Standardize on importing `olm-loader` rather than pasting the same boilerplate
in different tests. Importantly, `spec/unit/crypto.spec.js` did not include any
loading approach, so it would only find Olm if some other test loaded it first.
Signed-off-by: J. Ryan Stinnett <jryans@gmail.com>