Remove all dapp permissions related settings (#9120)

* Completely remove all dapps struct from rpc

* Remove unused pub use

* Remove dapp policy/permission func in ethcore

* Remove all dapps settings from rpc

* Fix rpc tests

* Use both origin and user_agent

* Address grumbles

* Address grumbles

* Fix tests

parity/lib.rs

@@ -79,9 +79,6 @@ extern crate log as rlog;
 #[cfg(feature = "secretstore")]
 extern crate ethcore_secretstore;
 
-#[cfg(feature = "dapps")]
-extern crate parity_dapps;
-
 #[cfg(test)]
 #[macro_use]
 extern crate pretty_assertions;