gallium/auxiliary/vl: Fix a couple of warnings

Remove unused functions and mark unhandled default case with
unreachable.

Signed-off-by: Kristian H. Kristensen <hoegsberg@google.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
14 jobs for !690 with warning-fixes in 10 minutes and 7 seconds (queued for 1 second)
detached
Status Job ID Name Coverage
  Containers Build
passed #250381
debian

00:00:16

 
  Build+Test
passed #250383
meson-clang

00:09:47

passed #250389
meson-gallium-clover-llvm

00:05:25

passed #250390
meson-gallium-clover-llvm39

00:04:39

passed #250388
meson-gallium-drivers-other

00:05:31

passed #250387
meson-gallium-radeonsi

00:04:43

passed #250391
meson-gallium-st-other

00:01:45

passed #250382
meson-gallium-swr

00:07:18

passed #250386
meson-glvnd

00:04:02

passed #250385
meson-loader-classic-dri

00:05:58

passed #250384
meson-vulkan

00:02:06

passed #250393
scons-llvm

00:03:41

passed #250392
scons-nollvm

00:02:59

passed #250394
scons-swr

00:05:38