Don't remove highlight of misspelled word on pdict save

Don't remove highlight of misspelled word on pdict save

* lisp/textmodes/ispell.el (ispell-pdict-save): Don't restart
flyspell-mode, as bug#11963, which this was supposed to fix, is
fixed better by ispell-command-loop, when the user types 'i' or
'a'.  Restarting Flyspell mode when the personal dictionary is
saved caused bug#31372 as side effect.
(ispell-command-loop): Test 'flyspell-mode', not whether
flyspell-unhighlight-at is fboundp, to determine whether Flyspell
mode is turned on in the current buffer.
(flyspell-unhighlight-at): Add declare-function form for it.