Remove DOMRequestState

- This CL replaces DOMRequestState in V8PromiseCustom with NewScriptState.
- This CL removes DOMRequestState, since it's no longer used.

BUG=357144

Review URL: https://codereview.chromium.org/238643002

git-svn-id: svn://svn.chromium.org/blink/trunk@171554 bbb929c8-8fbe-4397-9dbb-9b2b20218538