chore: Remove links to roadmap (#17554)

Discovered by
https://github.com/vectordotdev/vector/issues/17547#issuecomment-1570289321

We dropped the public roadmap as it seemed to be doing more harm than
good as it proved not to be
terribly accurate as priorities shift.

Signed-off-by: Jesse Szwedko <jesse.szwedko@datadoghq.com>

Signed-off-by: Jesse Szwedko <jesse.szwedko@datadoghq.com>