Why is there a mirrored Feedbin logo in the top right of the menu bar dropdown

This is the Feedbin logo, mirrored, and with some sesame seeds on top. I guess it's supposed to be a funny joke about hamburger menus, but it's _super_ unclear and probably infringing on something. Wherever [this icon](https://github.com/keybase/client/blob/master/shared/images/iconfont/140-kb-iconfont-nav-2-hamburger-24.svg) came from should probably be audited.

Start with shared/images/iconfont/140-kb-iconfont-nav-2-hamburger-24.svg, then inspect its history and where the hamburger icon is used in the menu bar dropdown. Confirm whether this asset produces the mirrored Feedbin-like image and determine the intended replacement or removal; done means the origin is understood and the unclear logo no longer appears.

Written by the indexing model from the issue text.