fix(build): remove unused variant package lists before lb build

live-build picks up ALL .list.chroot files in config/package-lists/.
After rsync, bee-nvidia.list.chroot, bee-amd.list.chroot, and
bee-nogpu.list.chroot all end up in BUILD_WORK_DIR — causing lb to
try installing packages from every variant (and leaving version
placeholders unsubstituted in the unused lists).

Fix: after copying bee-${BEE_GPU_VENDOR}.list.chroot → bee-gpu.list.chroot,
delete all other bee-{nvidia,amd,nogpu}.list.chroot from BUILD_WORK_DIR.

Also includes nomsi boot mode changes (bee-nvidia-load + grub.cfg).

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

iso/builder/config/bootloaders/grub-pc/grub.cfg

@@ -24,6 +24,11 @@ menuentry "EASY-BEE (NVIDIA GSP=off)" {
     initrd  @INITRD_LIVE@
 }
 
+menuentry "EASY-BEE (NVIDIA no MSI-X)" {
+    linux   @KERNEL_LIVE@ @APPEND_LIVE@ nomodeset bee.nvidia.mode=nomsi net.ifnames=0 biosdevname=0 mitigations=off transparent_hugepage=always numa_balancing=disable nowatchdog nosoftlockup
+    initrd  @INITRD_LIVE@
+}
+
 menuentry "EASY-BEE (fail-safe)" {
     linux   @KERNEL_LIVE@ @APPEND_LIVE@ bee.nvidia.mode=gsp-off memtest noapic noapm nodma nomce nolapic nosmp vga=normal net.ifnames=0 biosdevname=0
     initrd  @INITRD_LIVE@