bug#13312: 24.3.50; delete selection mode not killing on overwrite

[Juri Linkov]

> What was the reason for introducing
> `self-insert-uses-region-functions'?  It seems it was only for
> `electric-pair-mode'.  IIRC, I wasn't too happy with that hack when
> it was done.  Now it seems to be dirtying (complicating) `delsel.el'.
> Isn't there a better way?

I think (run-hook-with-args-until-success 'self-insert-uses-region-functions)
could be moved to the body of `delete-selection-helper'.
Then the users again will enjoy the simplicity of

  (put 'self-insert-command 'delete-selection t)

and

  (put 'self-insert-command 'delete-selection 'kill)

> Sorry, I cannot judge now whether this DTRT.  But again, this seems
> to reach beyond this bug.  (Let me know if I'm missing something
> and this is really specific to this bug.)

The first hunk of my patch fixes the reported bug.