Try to get grandpa tests compiling again (#1121)

* Revert "start to refactor block import wrapper a bit"

This reverts commit b919de49e1a82422a0870b66100832d531174771.

* Refactor grandpa stuff to get tests almost compiling

* Fixes after rebase

* Fixes merge compile errors

substrate/core/client/src/block_builder/block_builder.rs

@@ -39,7 +39,7 @@ impl<'a, Block, A> BlockBuilder<'a, Block, A>
 where
 	Block: BlockT<Hash=H256>,
 	A: ProvideRuntimeApi + HeaderBackend<Block> + 'a,
-	A::Api: BlockBuilderApi<Block> + Core<Block>,
+	A::Api: BlockBuilderApi<Block>,
 {
 	/// Create a new instance of builder from the given client, building on the latest block.
 	pub fn new(api: &'a A) -> error::Result<Self> {
@@ -84,7 +84,7 @@ where
 			block_id: &BlockId<Block>,
 			xt: Block::Extrinsic,
 			extrinsics: &mut Vec<Block::Extrinsic>
-		) -> error::Result<()> where T: BlockBuilderApi<Block> + Core<Block> {
+		) -> error::Result<()> where T: BlockBuilderApi<Block> {
 			api.map_api_result(|api| {
 				match api.apply_extrinsic(block_id, &xt)? {
 					Ok(ApplyOutcome::Success) | Ok(ApplyOutcome::Fail) => {