Speed up Eshell smart display module

Speed up Eshell smart display module

em-smart was forcibly re-displaying the screen upwards of 500 times
per screen of output.  This caused the Eshell to feel quite slow when
the module was in use.  By using fewer hooks and never explicitly
calling 'redisplay' (which was unnecessary) the performance issues go
away (bug#57367).

lisp/eshell/em-smart.el:

(em-smart-unload-hook, eshell-smart-unload-hook): Remove
'eshell-smart-scroll' instead of the now deleted
'eshell-refresh-windows'.

(eshell-smart-displayed, eshell-currently-handling-window)
(eshell-refresh-windows): Delete.

(eshell-smart-scroll-window): Rename to 'eshell-smart-scroll-windows'
and add a bunch of logic originally from 'eshell-refresh-windows'.

(eshell-smart-initialize): Don't add a hook onto
'window-scroll-functions'.  Replace 'eshell-refresh-windows' with
'eshell-smart-scroll-windows'.

(eshell-smart-display-setup): Don't refresh windows.

(eshell-smart-redisplay): Rename to 'eshell-smart-scroll'.  Delete
'eobp' case.