The `round_image()` function has the `icon_size` parameter, which is not
used by that function, because the size is determined from a pixbuf size.
Let's remove that redundant `icon_size` parameter.
accountsservice has 1 MB limit for avatars, however, users panels
refuses to show avatars bigger than 64 KB for some historical reasons.
But you can still successfully set avatars up to the accountsservice
limit. Let's remove this custom limit and other redundant check and
rely just on accountsservice limits and errors from GDK.
https://bugzilla.gnome.org/show_bug.cgi?id=792243
