Bug 1458308 - Remove app.update.auto and app.update.enabled from prefs.rs and marionette.js r=rstrong,ato

`app.update.auto` should actually never have been needed here. `app.update.disabledForTesting`, and before that, `app.update.enabled` will prevent updates altogether. Now that the `app.update.auto` pref is not the correct mechanism for disabling automatic update, this pref should be removed from these files.

`app.update.enabled` can also be removed from prefs.rs at this time as per the comment in the file indicating that it can be removed when Firefox 62 stabilizes.

Depends on D10315

Differential Revision: https://phabricator.services.mozilla.com/D10780

--HG--
extra : moz-landing-system : lando

testing/geckodriver/src/prefs.rs

@@ -12,14 +12,8 @@ lazy_static! {
         // Make sure Shield doesn't hit the network.
         ("app.normandy.api_url", Pref::new("")),
 
-        // Disable automatic downloading of new releases
-        ("app.update.auto", Pref::new(false)),
-
         // Disable automatically upgrading Firefox
         ("app.update.disabledForTesting", Pref::new(true)),
-        // app.update.enabled is being removed. Once Firefox 62 becomes stable,
-        // the line below can be removed as well.
-        ("app.update.enabled", Pref::new(false)),
 
         // Enable the dump function, which sends messages to the system
         // console

testing/marionette/components/marionette.js

@@ -56,12 +56,6 @@ const RECOMMENDED_PREFS = new Map([
   // Make sure Shield doesn't hit the network.
   ["app.normandy.api_url", ""],
 
-  // Disable automatic downloading of new releases.
-  //
-  // This should also be set in the profile prior to starting Firefox,
-  // as it is picked up at runtime.
-  ["app.update.auto", false],
-
   // Disable automatically upgrading Firefox.
   //
   // This should also be set in the profile prior to starting Firefox,