These two APIs originally were used to modify/control the "status bar" text at the bottom of browser windows. However, they have never had any actual effect on Chrome's status bar, and they are not standardized attributes. Gecko has not supported these attributes since version 23; WebKit still supports these attributes. The related window.status attribute *is* standardized, but also must never have an impact on the window status bar (https://html.spec.whatwg.org/multipage/window-object.html#dom-window-status). The window.status attribute is not being modified with this launch.
These are non-standard APIs that aren't implemented by all browsers and have no effect on browser behavior. This cleans them up, and removes a potential fingerprinting signal.