Merge Verifier into block_import.rs

These two files were largely the same, just hooking into sync structs 
with almost identical imports. As this project shapes up, removing dead 
weight is appreciated.

substrate/tendermint/client/src/lib.rs

@@ -22,7 +22,6 @@ mod validators;
 mod tendermint;
 pub use tendermint::TendermintAuthority;
 mod block_import;
-mod verifier;
 
 mod import_queue;
 use import_queue::TendermintImportQueue;