delete clover

there comes a time when a project has to be declared unfit to remain
in the tree

this frontend hasn't seen actual development in about 6 years

if someone has a pressing need to continue development, there's no
blocker to un-deleting it, but unless that happens, there's now a
more featureful, more conformant, more active CL frontend in the tree

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Reviewed-by: Karol Herbst <kherbst@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/19385>

.gitlab-ci/windows/mesa_build.ps1

@@ -53,7 +53,6 @@ meson setup `
 -Dvideo-codecs="all" `
 -Dgles1=enabled `
 -Dgles2=enabled `
--Dgallium-opencl=icd `
 -Dgallium-rusticl=false `
 -Dmicrosoft-clc=enabled `
 -Dstatic-libclc=all `