Stop Discourse from prompting for push notification on latest iOS beta
where the navigators exposes a broken Push object.
We had some feature detection functions that where outside our
pre-initializer that it dedicated for this stuff. All feature detection
now lives on sniff-capabilities file.
Also removed some old browser detection from the push notifications
code, and simplified the function signature because of it.
Co-authored-by: Jarek Radosz <jradosz@gmail.com>