perf: use polymophism instead duck test

src/util/assert.ts

@@ -1,6 +1,6 @@
 import { AssertionError } from './error'
 
-export default function (predicate: any, message?: string) {
+export default function<T> (predicate: T | null | undefined, message?: string) {
   if (!predicate) {
     message = message || `expect ${predicate} to be true`
     throw new AssertionError(message)

src/util/underscore.ts

@@ -36,10 +36,6 @@ export function toLiquid (value: any): any {
   return value
 }
 
-export function create<T1 extends object, T2 extends T1 = T1> (proto: T1): T2 {
-  return Object.create(proto)
-}
-
 export function isNil (value: any): boolean {
   return value === null || value === undefined
 }