gokrazy, tstest, cmd/vnet: switch amd64 kernel to gokrazy/kernel.amd64

The tailscale/gokrazy-kernel module was a fork of rtr7/kernel that
stalled at Linux 6.8.9 (July 2024). All of the kernel config options we
had added in that fork (ENA, Xen for EC2, virtio-mmio for qemu microvm,
virtio RNG, IPv6 policy routing, netlink diag, etc) are now present in
the gokrazy project's own gokrazy/kernel.amd64 module, which tracks
current kernel.org releases (Linux 7.1.3 as of this change) and is the
gokrazy project's supported kernel for x86_64 PCs and VMs.

Switch the tsapp and natlabapp images, the natlab VM tests, and the
CI workflow to gokrazy/kernel.amd64, drop the tailscale/gokrazy-kernel
dependency, and update gokrazy/kernel.arm64 to latest while here.

Verified with TestEasyEasy, TestJustIPv6, and TestTailscaleSSH in
tstest/natlab/vmtest with --run-vm-tests.

Updates #1866

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
Change-Id: I90c3765a4e18f5609b4d77b51ac38d17c8e3688a

cmd/vnet/run-krazy.sh

@@ -12,7 +12,7 @@ set -eux
 qemu-system-x86_64 -M microvm,isa-serial=off \
     -m 1G \
     -nodefaults -no-user-config -nographic \
-    -kernel $HOME/src/github.com/tailscale/gokrazy-kernel/vmlinuz \
+    -kernel $HOME/src/github.com/gokrazy/kernel.amd64/vmlinuz \
     -append "console=hvc0 root=PARTUUID=60c24cc1-f3f9-427a-8199-76baa2d60001/PARTNROFF=1 ro init=/gokrazy/init panic=10 oops=panic pci=off nousb tsc=unstable clocksource=hpet tailscale-tta=1 tailscaled.env=TS_DEBUG_RAW_DISCO=1 ${EXTRA_ARG}" \
     -drive id=blk0,file=$HOME/src/tailscale.com/gokrazy/natlabapp.img,format=raw \
     -device virtio-blk-device,drive=blk0 \