doc/next: delete

The release note fragments have been merged and added
as _content/doc/go1.24.md in x/website in CL 634056.

For #68545.

Change-Id: I7b3840df01b8c3699681c0cd21a16af70f74d31d
Reviewed-on: https://go-review.googlesource.com/c/go/+/634057
Auto-Submit: Michael Knyszek <mknyszek@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>

Author: gopherbot