Fixes #1628: Clean up UIConstants.colors (#1629)
Fixes #1628: Clean up UIConstants.colors (#1629)

* Remove currently unused colors

* Change photon hex to photon constant

mozilla-mobile/focus,mozilla/focus,justindarc/focus,mozilla-mobile/focus-ios,mozilla-mobile/focus-ios,justindarc/focus,mozilla-mobile/focus,mozilla-mobile/focus,justindarc/focus,mozilla-mobile/focus-ios,mozilla-mobile/focus,justindarc/focus,mozilla-mobile/focus,mozilla-mobile/focus-ios,justindarc/focus,mozilla-mobile/focus-ios,mozilla-mobile/focus-ios,mozilla/focus,mozilla/focus,mozilla/focus,mozilla-mobile/focus,justindarc/focus,mozilla/focus