Stop shipping a second kernel nobody boots

The live ISO boots one kernel for every machine, and after the preceding commit
that kernel is linux-t2. Stock linux is then a second kernel nobody boots, plus
its own archiso initramfs, copied into both the ISO tree and the
size-constrained FAT EFI image — about 147MB.

It could not simply be deleted: releng's broadcom-wl hard-depends on linux and
is the only releng package that does, so pacman would pull the kernel back in.

broadcom-wl is a prebuilt module for stock linux and cannot load on linux-t2.
It has kept working until now only because of the bug the preceding commit
fixes — the ISO has been booting stock all along — so it is booting T2 that
takes it away, not this commit. Dropping the package only stops shipping
something that can no longer load. Nothing in the offline install needs Wi-Fi
in the live environment.

Both packages stay in the offline mirror and this changes nothing about
installed systems: linux comes from builder/archinstall.packages and remains
what configurator's detect_kernel picks for every machine that is not a T2 Mac,
and broadcom-wl comes from omarchy-other.packages, so install/hardware/
fix-bcm43xx.sh can still install it offline on BCM4360/BCM4331 MacBooks.

The removal is anchored so linux-t2, linux-firmware, linux-firmware-marvell and
linux-atm are untouched; verified against releng's real list.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

builder/build-iso.sh

@@ -116,6 +116,19 @@ cp "/tmp/$NODE_FILENAME" "$build_cache_dir/airootfs/opt/packages/"
 arch_packages=(linux-t2 git gum jq openssl plymouth python-terminaltexteffects tzupdate omarchy-keyring "$OMARCHY_SETTINGS_PACKAGE" lvm2 cryptsetup parted)
 printf '%s\n' "${arch_packages[@]}" >> "$build_cache_dir/packages.x86_64"
 
+# The live ISO boots linux-t2 (see airootfs/etc/mkinitcpio.d/linux-t2.preset), so
+# stock linux is a second kernel nobody boots: ~147MB of ISO, plus its own archiso
+# initramfs, copied into both the ISO tree and the size-constrained FAT EFI image.
+#
+# It cannot just be deleted — releng's broadcom-wl hard-depends on it, and it is
+# the only releng package that does, so pacman would drag the kernel straight back
+# in. broadcom-wl is a prebuilt module for stock linux and cannot load on the
+# kernel we boot, so it has done nothing since we started booting T2 anyway. The
+# install is entirely offline and the live environment needs no Wi-Fi driver.
+#
+# Anchored so linux-t2 and linux-firmware are untouched.
+sed -i -E '/^(linux|broadcom-wl)$/d' "$build_cache_dir/packages.x86_64"
+
 # Build the offline mirror: everything pacstrap might want during the target
 # install. With --local-source, the omarchy* packages we just built are
 # already in the mirror and we filter them out below. Without it, pacman -Syw