Remove gpu_burn from ISO build — binary too large

gpu_burn requires CUDA toolkit (~4GB) to build and the resulting binary
would significantly inflate the ISO. Removed from vendor tool list and
smoketest. build-gpu-burn.sh dropped as well.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

iso/builder/smoketest.sh

@@ -38,13 +38,11 @@ for tool in dmidecode smartctl nvme ipmitool lspci audit; do
     fi
 done
 
-for tool in nvidia-smi gpu_burn; do
-    if p=$(PATH="/usr/local/bin:$PATH" command -v "$tool" 2>/dev/null); then
-        ok "$tool found: $p"
-    else
-        warn "$tool: NOT FOUND (optional but expected)"
-    fi
-done
+if p=$(PATH="/usr/local/bin:$PATH" command -v nvidia-smi 2>/dev/null); then
+    ok "nvidia-smi found: $p"
+else
+    fail "nvidia-smi: NOT FOUND"
+fi
 
 echo ""
 echo "-- NVIDIA modules --"