consensus/clique, core: API cleanup (#23100)

This removes some code:

- The clique engine calculated the snapshot twice when verifying headers/blocks.

- The method GetBlockHashesFromHash in Header/Block/Lightchain was only used by tests. It
  is now removed from the API.
  
- The method GetTdByHash internally looked up the number before calling GetTd(hash, num).
  In many cases, callers already had the number, and used this method just because it has a
  shorter name. I have removed the method to make the API surface smaller.

consensus/clique/clique.go

@@ -363,7 +363,7 @@ func (c *Clique) verifyCascadingFields(chain consensus.ChainHeaderReader, header
 		}
 	}
 	// All basic checks passed, verify the seal and return
-	return c.verifySeal(chain, header, parents)
+	return c.verifySeal(snap, header, parents)
 }
 
 // snapshot retrieves the authorization snapshot at a given point in time.
@@ -460,18 +460,12 @@ func (c *Clique) VerifyUncles(chain consensus.ChainReader, block *types.Block) e
 // consensus protocol requirements. The method accepts an optional list of parent
 // headers that aren't yet part of the local blockchain to generate the snapshots
 // from.
-func (c *Clique) verifySeal(chain consensus.ChainHeaderReader, header *types.Header, parents []*types.Header) error {
+func (c *Clique) verifySeal(snap *Snapshot, header *types.Header, parents []*types.Header) error {
 	// Verifying the genesis block is not supported
 	number := header.Number.Uint64()
 	if number == 0 {
 		return errUnknownBlock
 	}
-	// Retrieve the snapshot needed to verify this header and cache it
-	snap, err := c.snapshot(chain, number-1, header.ParentHash, parents)
-	if err != nil {
-		return err
-	}
-
 	// Resolve the authorization key and check against signers
 	signer, err := ecrecover(header, c.signatures)
 	if err != nil {