Remove all (non-dev) client references from frame, activate dependency enforcer (#4184)

* Move transaction pool to primitives

* move backend, errors into primitives

* remove unused client depencies

* Move rpc-api into primitives

* Move peerset back to client

* Move rpc/api back to client, move palette/support/rpc into utils

* move support-rpc into subfolder

* move system-rpc into utils

* move transaction-pool  and -graph back into client

* fix broken imports

* Clean up test primitives

* Make support test utils independent of frame

* remove unnecessary node dependencies from service

* Reactivate dependency script:
 - only enforce the now achieved status quo will remain
 - allow for primitives to depend on /client for now without failing
 - more discriptive error message so people understand, what it wants
 - minor fix to differentiative between ../client and /client (which may be a subfolder)
 - don't allow this to fail anylonger.

* fix doc comment

* 'Should not' rather than 'must not'.

* Revert unwanted dependency changes

* fix faulty import

* fixup derive_more version

* fix wrong import path

substrate/client/finality-grandpa/src/observer.rs

@@ -156,7 +156,7 @@ pub fn run_grandpa_observer<B, E, Block: BlockT<Hash=H256>, N, RA, SC>(
 	link: LinkHalf<B, E, Block, RA, SC>,
 	network: N,
 	on_exit: impl Future<Item=(),Error=()> + Clone + Send + 'static,
-) -> ::client_api::error::Result<impl Future<Item=(),Error=()> + Send + 'static> where
+) -> ::sp_blockchain::Result<impl Future<Item=(),Error=()> + Send + 'static> where
 	B: Backend<Block, Blake2Hasher> + 'static,
 	E: CallExecutor<Block, Blake2Hasher> + Send + Sync + 'static,
 	N: Network<Block> + Send + Sync + 'static,