Remove TransientValidationData (#2272)

* collation-generation: use persisted validation data

* node: remote FullValidationData API

* runtime: remove FullValidationData API

* backing tests: use persisted validation data

* FullCandidateReceipt: use persisted validation data

This is not a big change since this type is not used anywhere

* Remove ValidationData and TransientValidationData

Also update the guide

polkadot/roadmap/implementers-guide/src/runtime-api/full-validation-data.md

@@ -1,7 +0,0 @@
-# Full Validation Data
-
-Yields the full [`ValidationData`](../types/candidate.md#validationdata) at the state of a given block.
-
-```rust
-fn full_validation_data(at: Block, ParaId, OccupiedCoreAssumption) -> Option<ValidationData>;
-```