ec2-desktop: Don't enable firstboot_pkgs

We don't have any packages to install by default when the instance
first boots, so (as with the "small" flavour) don't enable the
firstboot_pkgs script.  If someone wants to launch a desktop with
packages autoinstalled at first boot, they can enable the script at
the same time as they provide the list of packages.

Sponsored by:	Amazon

release/tools/ec2-desktop.conf

@@ -24,7 +24,7 @@ export VM_EXTRA_PACKAGES="${VM_EXTRA_PACKAGES} amazon-ssm-agent ec2-scripts \
 # Services to enable in rc.conf(5).
 export VM_RC_LIST="${VM_RC_LIST} ec2_configinit ec2_ephemeral_swap \
     ec2_fetchkey ec2_setpass ec2_loghostkey firstboot_pkg_upgrade \
-    firstboot_pkgs growfs growfs_postboot sshd dbus xrdp xrdp_sesman"
+    growfs growfs_postboot sshd dbus xrdp xrdp_sesman"
 
 vm_extra_pre_umount() {
 	# Limit firstboot_pkg_upgrade to the base system.