Revert "input.conf: bind MBTN_MID to align-to-cursor"

It can be too easy to change the video position without a single way to
undo the change. Also, this is mostly useful for images. Binding can be
brought back in a better way with an image profile or another method
that is more resistant to accidental clicks.

This reverts commit e98d3b62ec52fdad550a94635c38cc4bf22cc310.