Change extrinsic_count to extrinsic_index in pallet-utility (#5044)

Co-authored-by: Benjamin Kampmann <ben.kampmann@googlemail.com>

substrate/frame/utility/src/lib.rs

@@ -538,7 +538,7 @@ impl<T: Trait> Module<T> {
 	pub fn timepoint() -> Timepoint<T::BlockNumber> {
 		Timepoint {
 			height: <system::Module<T>>::block_number(),
-			index: <system::Module<T>>::extrinsic_count(),
+			index: <system::Module<T>>::extrinsic_index().unwrap_or_default(),
 		}
 	}