Add transparency to logo images on the brand assets page

[tquirino]

The current PNG files don't have a transparent background. This makes it more difficult to use the Remix logo. I've re-exported each image to fix this, so that they all have transparent backgrounds.

[brookslybrand]

Sweet! Will you delete the old files and update the name of each of the new files? That will allow users to download the correct asset from the brand page

Also, will you remove the background from each of the SVGs? Those might be easier to just re-export from the figma file