Remove support or native Select element Size/Multiple variants

[endigo9740]

See this issues for details on why these will no longer be supported:

• https://github.com/skeletonlabs/skeleton/issues/3534

In a nutshell, it seems browser vendors are moving away from support for these rather niche use cases. Neither are really properly supported on mobile, so we should lean into a custom component to supplement and replace these interfaces.

Thankfully Zag.js now includes a dedicated Listbox component:

• https://zagjs.com/components/react/listbox
• https://zagjs.com/components/svelte/listbox

This will be implemented in Skeleton as part of:

• https://github.com/skeletonlabs/skeleton/issues/3551

[endigo9740]

Note that as part of yesterday's v4 launch these select element styles have not been removed from the core package, but are no longer advertised on the documentation. We will plan to remove these in the next major release. However, we strongly advise all users migrate to the brand new Listbox component as the replacement for this feature.