[Docs Rewrite] Remove "Feedback" page

[markerikson]

What docs page is being added or updated?

• Section: Other
• Page: Feedback

Parent issue: #3602

For Updating Existing Content

What updates should be made to the page?

Remove the "Feedback" page entirely. We never bothered using Product Pains / Canny at all.

For future reference, that link is:

https://redux.canny.io/feature-requests/

As an alternative, we can add a "Feedback" link that points directly to the "New Issue" URL on Github.

I suppose we could hypothetically change the content to say "leave an issue or contact us in Reactiflux/Twitter", but I don't think it's worth it.

Tasks

• Remove the Feedback page
• Add a "Feedback" link in the bottom section that points to the "Help and Discussion" section, and maybe add a "Leave an issue" link there too.