Remove stale autoexec.ipxe when Secure Boot generation is disabled

Prevent a leftover autoexec.ipxe from a previous build with
generate_disks_secureboot enabled from being included in checksums
and release assets when the flag is later turned off.

roles/netbootxyz/tasks/generate_disks.yml

@@ -40,3 +40,10 @@
   when:
     - generate_disks_secureboot | default(false) | bool
     - bootloader_filename == "netboot.xyz"
+
+- name: Remove stale autoexec.ipxe when Secure Boot is disabled
+  ansible.builtin.file:
+    path: "{{ netbootxyz_root }}/ipxe/autoexec.ipxe"
+    state: absent
+  when:
+    - not (generate_disks_secureboot | default(false) | bool)