Bug 1837813 - Remove unused signon.* prefs r=geckoview-reviewers,m_kato

Depends on D180601

Differential Revision: https://phabricator.services.mozilla.com/D180602

mobile/android/app/mobile.js

@@ -78,9 +78,6 @@ pref("browser.helperApps.deleteTempFileOnExit", false);
 
 /* password manager */
 pref("signon.firefoxRelay.feature", "not available");
-pref("signon.rememberSignons", true);
-pref("signon.expireMasterPassword", false);
-pref("signon.debug", false);
 
 /* form helper (scroll to and optionally zoom into editable fields)  */
 pref("formhelper.autozoom", true);