tests/linux: cleanup missing cpus in nvidiagpunumanodes

Some cpus were removed from /sys/devices/system/cpu to reduce the size
of the topology, but the corresponding symlinks in /sys/bus/cpu/devices
were still there.
This causes these cpu to appear as offline when discovering through
/sys/bus/cpu/devices (while they don't exist at all), and to not
appear at all when discovering through /sys/devices/system/cpu.

Remove the broken symlinks so that discovery from both directory sees
the same (reduced) cpuset.

Signed-off-by: Brice Goglin <Brice.Goglin@inria.fr>

tests/hwloc/linux/nvidiagpunumanodes.kept.output

@@ -106,5 +106,4 @@ Relative latency matrix (name NUMALatency kind 5) between 8 NUMANodes (depth -3)
      1    80    80    80    80    80    10    80    80
      2    80    80    80    80    80    80    10    80
      3    80    80    80    80    80    80    80    10
-144 processors not represented in topology: 0x0000ffff,0xffffffff,0xffffff00,0x00ffffff,0xffffffff,0xffff0000
 Topology not from this system

tests/hwloc/linux/nvidiagpunumanodes.output

@@ -94,5 +94,4 @@ Relative latency matrix (name NUMALatency kind 5) between 2 NUMANodes (depth -3)
  index     0     1
      0    10    40
      1    40    10
-144 processors not represented in topology: 0x0000ffff,0xffffffff,0xffffff00,0x00ffffff,0xffffffff,0xffff0000
 Topology not from this system