Generalise type of deleteBy

[Henning Thielemann]

On Sun, 11 Sep 2016, Matthew Pickering wrote:

> The type of `deleteBy` in `Data.List` could easily be generalised in a
> useful way.
>
> ```
> deleteBy :: (a -> a -> Bool) -> a -> [a] -> [a]
> ```

I do not see why deleteBy should have an argument for the deleted element, 
anyway, since it is not even the element to delete (only an equivalent 
one). Wouldn't a function with type

newDeleteBy :: (a -> Bool) -> [a] -> [a]

be much more straight-forward?