Bug 1827971 - Remove OPEN_FIREFOX_VIEW_AND_COLORWAYS_MODAL SpecialMessageAction r=omc-reviewers,aminomancer

Turns out both `OPEN_FIREFOX_VIEW` and `OPEN_FIREFOX_VIEW_AND_COLORWAYS_MODAL` just call `window.FirefoxViewHandler.openTab();`, so not only is this action kinda misleading now that the Colorways closet is gone, it's a duplicate action.

Differential Revision: https://phabricator.services.mozilla.com/D175792