Unless you have enabled the Google search suggestions option no data is transferred to the search engine. The text just provides context as to what selecting that search engine will do.

We are looking into ways to make installing and removing search engines from the browser simpler. Though for right now one can only add and disable and change the default search engine.

You can still disable the search engines if you have root access to your device. Specifically, you need to pull and modify the file search.json. On my device, I have:

adb pull /data/data/org.mozilla.firefox/files/mozilla/rbn69ru0.default/search.json

Now, by default, this file doesn't format everything nicely, so you can use something like

http://jsonformat.com

In order to clean things up. In any case, you'll see bits such as

              "_id": "[app]/bing.xml",
              "_name": "Bing",
              "_hidden": false,
              "description": "",
              "__searchForm": "http://www.bing.com",

You need to take the "_hidden" flag and change it to true. Do this for all of the search engines to hide all of them. Or, frankly, just delete everything under engines. Then, upload the file back and restart firefox with a command like:

adb push search.json /data/data/org.mozilla.firefox/files/mozilla/rbn69ru0.default/

Until an application restart, the changes won't be seen.

As a slight editorial note, it's dumb that we have to do this by hand. Either we should be able to disable things under Settings->Customize->Search settings or we should have some way of turning things off in about:config. While I understand that removing menu items that cause too many support issues, completely removing the option even from about:config is counterproductive.