Remove network.http.sendSecureXSiteReferrer pref when Firefox 52 is released

[Gitoffthelawn]

network.http.sendSecureXSiteReferrer will no longer exist as of Firefox 52. See:
https://bugzilla.mozilla.org/show_bug.cgi?id=1308725
pyllyukko/user.js#190

As of Firefox 52, network.http.sendRefererHeader and network.http.referer.trimmingPolicy will be the only prefs to control this behavior. Both of those prefs are already available in this extension.

[schomery]

The new WebExtension version will blur those prefs that are not supported;
#80

[Gitoffthelawn]

Do you think it's best to blur them or hide them?

[jawz101]

I'd only support >= the latest stable releases of mobile and desktop Firefox. When I see deprecated prefs preserved in this add-on it sometimes gives me the impression it's not up-to-date even though it clearly is.

Or at least have entries say things like "desktop only", "deprecated in version x", "new in version x"