Bug 40788: Prevent nsIURLQueryStrippingListService from calling home when it is not enabled.

The URL query stripping service is enabled only in nightly builds,
still it is initialized and remote settings are downloaded.
This adds a condition that prevents the service from being initialized
if disabled.

Upstream Bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1812594
We should remove this patch if Mozilla decides that this is a problem
also for them, or if they do not but we decide to use the feature.