bug#33282: ImageMagick delegates

[Juri Linkov <juri@linkov.net>]

>> WebP is an image format that is gaining popularity,
>> but currently can't be displayed by image-mode.
>
> I wonder -- do you think its popularity merits Emacs getting native
> support for it?  I don't think I've seen too many sites that serve out
> WebP only, but perhaps that'll change now what Chrome is the only web
> browser people care about.

I tried to open https://developers.google.com/speed/webp/gallery
in EWW and it displays images.  Then I clicked the right mouse button
to use the image context menu to open it in a new tab, but there is
no such menu in EWW yet (I could implement "Open image in new tab"
in EWW after merging the tabs branch).  But it seems the web server
returns PNG images when the web client doesn't support WebP format.

>> I tried GetDelegateList, but it returned some delegates on whose
>> calling MagickRelinquishMemory caused a crash during bootstrapping.
>> There is no crash when calling MagickRelinquishMemory not during
>> bootstrapping, and I have no idea what is wrong.
>
> Perhaps if you post the gdb backtrace, somebody here has an idea.

Since Emacs no longer defaults to using ImageMagick, there is no point
in trying to implement ImageMagick support for WebP anymore.  Regarding
native support, if web servers return more widespread formats as fallback
when WebP is not supported on client, then there is not much need in WebP.