polkadot: eradicate LeafStatus (#1565)

Fixes #768.

Cargo.lock

@@ -3892,7 +3892,6 @@ dependencies = [
  "sc-service",
  "sc-tracing",
  "sc-utils",
- "schnellru",
  "sp-api",
  "sp-consensus",
  "sp-consensus-babe",
@@ -12527,7 +12526,6 @@ dependencies = [
  "polkadot-primitives-test-helpers",
  "prioritized-metered-channel",
  "sc-client-api",
- "schnellru",
  "sp-api",
  "sp-core",
  "tikv-jemalloc-ctl",
@@ -12914,7 +12912,6 @@ dependencies = [
  "sc-telemetry",
  "sc-transaction-pool",
  "sc-transaction-pool-api",
- "schnellru",
  "serde",
  "serde_json",
  "serial_test",