bug#19129: 25.0.50; recenter-positions is missing a reference to move-to-window-line-top-bottom

[Drew Adams]

> in the documentation for recenter-positions was forgotten that it is
> also used in move-to-window-line-top-bottom.  I added below patch as
> an illustration.

Actually no. The doc for a function should rarely, if ever, speak
about users (callers) of that function. It should simply say what
the function does, and perhaps what it can be used for if it is
intended for users.

But it should typically not try to list all of its callers, or even
the most important callers.

If this is no longer just a helper for `recenter-top-bottom'
then perhaps reference to even that function can be removed
from the `recenter-positions' doc.