On mobile devices like tablets or toasters the "Persistent Chat"
floating widget is already hidden.
So, the related checkbox available from the top navigation bar
is just confusing on tablet and mobile devices / toasters, since
that nice checkbox does nothing there.
On mobile and tablet, this is the graphical change:
| Before | After |
|----------|-----------|
|{F281239} | {F281235} |
This change do not change anything for desktop devices.
So, on desktop, that checkbox is obviously still visible.
Closes T15240