internal/poll: remove fd field from Windows' poll.operation
There is no need to keep the fd in the poll.operation struct,
given that all usages of this field have direct access to the fd struct.
This skims down the size of os.File by 16 bytes.
Change-Id: I837e345250387f62e294cc1772d752865a04ef6d
Reviewed-on: https://go-review.googlesource.com/c/go/+/685415 Reviewed-by: Damien Neil <dneil@google.com> Reviewed-by: Michael Knyszek <mknyszek@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Michael Knyszek <mknyszek@google.com>