vk/util: drop no-op compiler warning workaround

vk/util: drop no-op compiler warning workaround

`-Wswitch` applies to `switch()`, not `case:`, and is bypassed by the
presence of a `default:` anyway, so let's drop the `default:` and move
the warning suppression to where it can make a difference, and then it
turns out that we don't need to keep a list of special cases anymore :)

Signed-off-by: Eric Engestrom <eric.engestrom@intel.com>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>