[META] Update Drupal Brand Guidelines

The brand guidelines are now part of the Drupal DAM: https://drupal.widencollective.com/portals/gfvztttq/BrandPortal

And the brand narrative can be found here: https://docs.google.com/document/d/1x27NmbhpLYd0p8WZ19ntm_4P1TxNklPd35gz...