lib: replace Symbol.asyncIterator by SymbolAsyncIterator

Just replaced every Symbol.asyncIterator by SymbolAsyncIterator in the lib/* folder For this, i just have added SymbolAsyncIterator in the import

const {
  SymbolAsyncIterator,
} = primordials;

Of course i have removed unused import of Symbol 😄 I hope this pull request will help you ! :P