Remove erc-fill binding for cycling visual movement

Remove erc-fill binding for cycling visual movement

* etc/ERC-NEWS: Announce removal of troublesome key binding first
introduced in ERC 5.6 as part of the `erc-fill-wrap' module.
* lisp/erc/erc-fill.el (erc-fill-wrap-mode-map): Remove key binding for
`erc-fill-wrap-cycle-visual-movement'.
* test/lisp/erc/erc-fill-tests.el (erc-fill-wrap-visual-keys--body)
(erc-fill-wrap-visual-keys--prompt): Replace "C-c a" key simulations.
(Bug#73553)

(cherry picked from commit e3c45b9d707db824588e2bd9ae34c05911dfcc5a)