Delete some dead code from the `clips_window` module.
Delete some dead code from the `clips_window` module.

The functions that moved up and down by one row of clips were unused.
The operations were also semantically problematic, since it wasn't clear
what should happen to the selection (which is defined in terms of the
current page) when one moved up or down by one row.
HaroldMills/Vesper,HaroldMills/Vesper,HaroldMills/Vesper,HaroldMills/Vesper,HaroldMills/Vesper