bug#81578: 32.0.50; completion-eager-display + completion-eager-update breaks cycling + automatic tab completion

> Not sure why you have those expectations.  These two variables seem to
> be about updating the *Completions* buffer display and nothing else.
>
> Spencer and Juri, any comments?

I see that both reported cases are not regressions.
They exhibit the same behavior as in the released Emacs 30.

Here are slightly modified recipes for Emacs 30:

* Bug One

- $ mkdir -p a/b/c
- $ cd a
- Press C-x C-f
- Press ? to display the Completions buffer
- Press TAB twice

Observed behavior:

- The first tab appends "b/" to the minibuffer
- The second tab does nothing
- The minibuffer displays "/path/to/a/b/"
- Further tab presses do nothing

This behavior can be customized by different values of
'completion-auto-help'.

* Bug Two

- $ mkdir -p a/b
- $ mkdir -p a/c
- $ cd a
- Press C-x C-f
- Press TAB twice

Observed behavior:

- The first tab shows the message "[Complete, but not unique]"
- The second tab shows the Completions buffer

This behavior can be customized by 'completion-cycle-threshold'.