"DuckDuckGoOnion" is a weird naming format for onion search engines

At some point, we seem to have adopted this naming convention for default search engine options provided over onions in Tor Browser.

For example, on desktop we have:

• DuckDuckGoOnion
• BlockchairOnion

and on Android:

• DuckDuckGoOnion

Our naming conventions for onion sites can be inconsistent at best, but I think "DuckDuckGo onion" would be an improvement, and "DuckDuckGo onion site" seems like the most official way to describe an onion search engine (see Glossary / onion site).

Agreed new format

• DuckDuckGo (.onion)
• Startpage (.onion)
• Etc.