There are way too many preexisting scripts that rely on this behavior
for video panning, like for example scripts that allow you to use mpv as
an image viewer. If this behavior is desired then it may be better to
add a new option for panning relative to the destination instead.
The restriction of video-pan-x/y being clamped to {-3, 3} also results
in the video being impossible to pan if it was zoomed in beyond a
certain degree.
This reverts commit 7d6f9e3739.