toolkit.telemetry.cachedClientID, closes #739

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user.js

@@ -230,7 +230,6 @@ user_pref("toolkit.telemetry.unified", false);
 user_pref("toolkit.telemetry.enabled", false); // see [NOTE] above FF58+
 user_pref("toolkit.telemetry.server", "data:,");
 user_pref("toolkit.telemetry.archive.enabled", false);
-user_pref("toolkit.telemetry.cachedClientID", "");
 user_pref("toolkit.telemetry.newProfilePing.enabled", false); // [FF55+]
 user_pref("toolkit.telemetry.shutdownPingSender.enabled", false); // [FF55+]
 user_pref("toolkit.telemetry.updatePing.enabled", false); // [FF56+]