test: consolidate test helpers (#169)

* test: build transactions without using tree

* test: hashchains can be acquired from TransactionBuilder

* test: Remove obsolete TestTreeState code from integration test

* test: Extend transaction builder capabilities

* test: Replace TestTreeState with TransactionBuilder in KeyDirectoryTreeUnitTests

* test: extend capabilities to create invalid transactions

* test: remove TestTreeState

Author: jns-ps

crates/common/src/lib.rs

@@ -8,7 +8,5 @@ pub mod tree;
 #[macro_use]
 extern crate log;
 
-#[cfg(feature = "test_utils")]
-pub mod test_utils;
 #[cfg(feature = "test_utils")]
 pub mod transaction_builder;