Now there is a variable completions-highlight-face. When nil highlight
is disabled, otherwise it must be a the face to use, by default
completions-highlight.
I had the mode before because I needed some initialization, but with the
cursor-face feature that is not needed and the code got simpler.
Thanks, highlighting works correctly when the current buffer is *Completions*.
But cursor-face is not highlighted in *Completions* when the current buffer
is the minibuffer. Such highlighting is necessary when completions
are navigated from the minibuffer.