Hide Media Output from Volume Panel on Desktop

Desktop is using Headless System User Mode (HSUM). And MediaRouter2 is
not compatible with HSUM, causing Media Output to be broken. We need to
hide this component, and let users select input/output devices from the
settings page.

Bug: b/390286295, b/372868909
Test: mp sysuititan
Flag: EXEMPT desktop only changes
Change-Id: Ic326362e25747fb214877ca99cf7d271e7b0ad24