Network sync refactoring (part 1) (#11303)

* Remove unnecessary imports, move one internal re-export into where it is actually used, make one import explicit

* Move a few data structures down into modules

* Use generic parameters in `sc-network` instead of `chain::Client` trait

* Remove unnecessary bound

substrate/client/network/src/lib.rs

@@ -245,7 +245,6 @@
 //! More precise usage details are still being worked on and will likely change in the future.
 
 mod behaviour;
-mod chain;
 mod discovery;
 mod peer_info;
 mod protocol;