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>
10 jobs for !927 with vkutil-switch in 6 seconds (queued for 1 second)
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canceled debian #314131


skipped meson-clang #314133
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skipped meson-swr-glvnd #314132
skipped meson-vulkan #314138
skipped scons-llvm #314140
skipped scons-nollvm #314139
skipped scons-swr #314134
skipped scons-win64 #314135