Simplify BABE pre-digest definitions (#5289)

* Init vrf crate without type alias

* Generic PreDigest definition for BABE

* Fix BABE vrf interface change

* Missing default-features def in sp-consensus-babe

* Fix sp-consensus-babe compile

* frame-babe: fix type inference

* Unify type definitions of vrf output/proof and randomness

* frame-babe: fix tests

* Bump node impl version

* Update cargo lock

* Derive Copy for RawVRFOutput and RawVRFProof

* Fix duplicated derive

Co-authored-by: Gavin Wood <gavin@parity.io>