rpc/gasprice: remove unused Oracle state fields (#18352)

Author: VolodymyrBg

rpc/gasprice/gasprice.go

@@ -57,8 +57,6 @@ type Cache interface {
 // blocks. Suitable for both light and full clients.
 type Oracle struct {
 	backend     OracleBackend
-	lastHead    common.Hash
-	lastPrice   *big.Int
 	maxPrice    *big.Int
 	ignorePrice *big.Int
 	cache       Cache
@@ -102,7 +100,6 @@ func NewOracle(backend OracleBackend, params gaspricecfg.Config, cache Cache, lo
 
 	return &Oracle{
 		backend:          backend,
-		lastPrice:        params.Default,
 		maxPrice:         maxPrice,
 		ignorePrice:      ignorePrice,
 		checkBlocks:      blocks,