st/mesa: Clear texture's views when texture is removed from Shared->TexObjects

st/mesa: Clear texture's views when texture is removed from Shared->TexObjects

If texture is shared between several contexts, calling glDeleteTextures
will remove it from ctx->Shared->TexObjects - which makes impossible for
contexts, when destroyed, to release their views to this texture. Which
leaves dangling pointers to destroyed contexts.

Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/2960
Signed-off-by: Danylo Piliaiev <danylo.piliaiev@globallogic.com>
Reviewed-by: Tapani Pälli <tapani.palli@intel.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5106>