Remove ability to subscribe to newsletter on Cognitive community

[Oanh-and-only-Oanh]

Remove the bottom section of the Cognitive community page that allows user to opt into receiving newsletter.

See below.

[SathyaJayabal]

verified on dev

[Oanh-and-only-Oanh]

@kiril, let's release this when you come back from vacation in 2 weeks. FYI @SathyaJayabal @lakshmiathreya