spirv: always expose SpvCapabilityStorageImageExtendedFormats

I forgot to do this in commit 76b97d544e ("anv: enable storage image
extended formats"). Since both drivers support this now, no need for the
conditional enable.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Dave Airlie <airlied@redhat.com>

src/compiler/spirv/nir_spirv.h

@@ -42,7 +42,6 @@ struct nir_spirv_specialization {
 };
 
 struct nir_spirv_supported_extensions {
-   bool storage_image_extended_formats;
    bool image_ms_array;
 };