fix(reactivity): fix shallow readonly behavior for collections (#3003)

fix #3007

packages/reactivity/__tests__/readonly.spec.ts

@@ -7,7 +7,6 @@ import {
   markRaw,
   effect,
   ref,
-  shallowReadonly,
   isProxy,
   computed
 } from '../src'
@@ -455,32 +454,4 @@ describe('reactivity/readonly', () => {
       'Set operation on key "randomProperty" failed: target is readonly.'
     ).toHaveBeenWarned()
   })
-
-  describe('shallowReadonly', () => {
-    test('should not make non-reactive properties reactive', () => {
-      const props = shallowReadonly({ n: { foo: 1 } })
-      expect(isReactive(props.n)).toBe(false)
-    })
-
-    test('should make root level properties readonly', () => {
-      const props = shallowReadonly({ n: 1 })
-      // @ts-ignore
-      props.n = 2
-      expect(props.n).toBe(1)
-      expect(
-        `Set operation on key "n" failed: target is readonly.`
-      ).toHaveBeenWarned()
-    })
-
-    // to retain 2.x behavior.
-    test('should NOT make nested properties readonly', () => {
-      const props = shallowReadonly({ n: { foo: 1 } })
-      // @ts-ignore
-      props.n.foo = 2
-      expect(props.n.foo).toBe(2)
-      expect(
-        `Set operation on key "foo" failed: target is readonly.`
-      ).not.toHaveBeenWarned()
-    })
-  })
 })