Remove Pocket assests

[stephaniehobson]

https://getpocket.com/farewell

[janbrasna]

Some support, legal or other more permanent surfaces might still use it for a bit longer, TODO: check where it is used outside of just marketing/content, if that breaks anyone past Oct 8. (Logos, icons, social, favicons, components, …)

[stephaniehobson]

Anyone who needs them can make local copies. I expect the trademark page will want to keep them, for example.