Remove incorrect implementation of DataStoreReadOps

Previously, the function would try to block the whole thread whenever
requesting something from other peers.

This wasn't noticed since the implementation is only used in light
clients that were **NOT** compiled for WASM.

I noticed this implementation when reviewing #3159, which would have
caused these thread blockings to continue for longer times.

consensus/src/consensus/remote_data_store.rs

@@ -303,22 +303,8 @@ impl<N: Network> RemoteDataStore<N> {
 
 impl<N: Network> DataStoreReadOps for RemoteDataStore<N> {
     fn get<T: Deserialize>(&self, key: &KeyNibbles) -> Option<T> {
-        let proof = futures_executor::block_on(Self::get_trie(
-            Arc::clone(&self.network),
-            self.blockchain.clone(),
-            &[key.clone()],
-            self.min_peers,
-        ))
-        .ok();
-        if let Some(mut proof) = proof {
-            if proof.len() != 1 {
-                log::error!(len = proof.len(), "Unexpected amount of proved items");
-                None
-            } else {
-                proof.remove(key).flatten()
-            }
-        } else {
-            None
-        }
+        unimplemented!(
+            "this function is not implementable: a sync function cannot call an async one",
+        );
     }
 }