Finish migration to v2 primitives (#5037)

* remove v0 primitives from polkadot-primitives

* first pass: remove v0

* fix fallout in erasure-coding

* remove v1 primitives, consolidate to v2

* the great import update

* update runtime_api_impl_v1 to v2 as well

* guide: add `Version` request for runtime API

* add version query to runtime API

* reintroduce OldV1SessionInfo in a limited way

polkadot/runtime/metrics/src/with_runtime_metrics.rs

@@ -23,7 +23,7 @@
 const TRACING_TARGET: &'static str = "metrics";
 
 use parity_scale_codec::Encode;
-use primitives::v1::{
+use primitives::v2::{
 	metric_definitions::{CounterDefinition, CounterVecDefinition},
 	RuntimeMetricLabelValues, RuntimeMetricOp, RuntimeMetricUpdate,
 };

polkadot/runtime/metrics/src/without_runtime_metrics.rs

@@ -18,7 +18,7 @@
 //! provide a dummy implementation for the native runtime to avoid cluttering the runtime code
 //! with `#[cfg(feature = "runtime-metrics")]`.
 
-use primitives::v1::metric_definitions::{CounterDefinition, CounterVecDefinition};
+use primitives::v2::metric_definitions::{CounterDefinition, CounterVecDefinition};
 
 /// A dummy `Counter`.
 pub struct Counter;