fix(reactivity): should not trigger length dependency on Array delete

close #774

packages/reactivity/src/effect.ts

@@ -196,7 +196,7 @@ export function trigger(
     // also run for iteration key on ADD | DELETE | Map.SET
     if (
       type === TriggerOpTypes.ADD ||
-      type === TriggerOpTypes.DELETE ||
+      (type === TriggerOpTypes.DELETE && !isArray(target)) ||
       (type === TriggerOpTypes.SET && target instanceof Map)
     ) {
       const iterationKey = isArray(target) ? 'length' : ITERATE_KEY