zle: don't override *delete* and *kill*

[eras]

This restores the ability to consecutively delete (ie.) words and
have them come back consecutively in the next yank.

[danielshahaf]

This PR is intended to fix #150

[nicoulaj]

(Closing/reopening to trigger continuous integration)

[vincentbernat]

Another possibility is to restore kill/yank flags for the impacted ZLE widgets.

zle -f kill
zle -f yankbefore
zle -f yank

[danielshahaf]

@vincentbernat Yeah, that's discussed in #150 (comment) and subsequent comments.

Presently the priority is to merge redrawhook, which should fix these issues as well under zsh 5.9. Related issues include #418, #579, and #735.

The proof-of-concept patch in the linked comment will nevertheless be good to merge, as it will fix this issue under zsh versions that have zle -f but won't use redrawhook. (zle -f was introduced in 5.2; zle-line-pre-redraw in 5.3; and memo= will be introduced in 5.9.) Does that patch introduce any regressions? Off the top of my head, as written it will cause stderr spam on zsh versions too old to have zle -f.

I haven't the brainwidth to pursue this myself.