chore(vapor): remove setBlockKey multi-root warning path

packages/runtime-vapor/__tests__/helpers/setKey.spec.ts

@@ -59,8 +59,5 @@ describe('helpers: setBlockKey', () => {
 
     expect(blocks[0].$key).toBeUndefined()
     expect(blocks[1].$key).toBeUndefined()
-    expect(
-      `key cannot be applied to multiple root elements.`,
-    ).toHaveBeenWarned()
   })
 })

packages/runtime-vapor/src/helpers/setKey.ts

@@ -1,5 +1,4 @@
 import { isArray } from '@vue/shared'
-import { warn } from '@vue/runtime-dom'
 import type { Block } from '../block'
 import { isVaporComponent } from '../component'
 
@@ -17,8 +16,6 @@ export function setBlockKey(
   } else if (isArray(block)) {
     if (block.length === 1) {
       setBlockKey(block[0], key)
-    } else if (__DEV__ && block.length > 1) {
-      warn(`key cannot be applied to multiple root elements.`)
     }
   } else {
     block.$key = key