devel/vulkan-tools: unbreak vkcube-wayland

Sway dropped wl_shell support. Upstream had xdg-shell for some time
but reverted due to being "incompatible" with Weston.

• thread #1, name = 'vkcube-wayland', stop reason = signal SIGSEGV: invalid address (fault address: 0x0) frame #0: 0x00000008002625a3 libwayland-client.so.0`wl_proxy_marshal_constructor(proxy=0x0000000000000000, opcode=0, interface=0x00000000002152b8) at wayland-client.c:830:41 827 va_list ap; 828 829 va_start(ap, interface);

-> 830 wl_argument_from_va_list(proxy->object.interface->methods[opcode].signature,

831                                   args, WL_CLOSURE_MAX_ARGS, ap);
832          va_end(ap);
833

(lldb) bt

• thread #1, name = 'vkcube-wayland', stop reason = signal SIGSEGV: invalid address (fault address: 0x0)
  • frame #0: 0x00000008002625a3 libwayland-client.so.0`wl_proxy_marshal_constructor(proxy=0x0000000000000000, opcode=0, interface=0x00000000002152b8) at wayland-client.c:830:41 frame #1: 0x000000000020e822 vkcube-wayland`wl_shell_get_shell_surface(wl_shell=0x0000000000000000, surface=0x0000000800a22090) at wayland-client-protocol.h:2926:7 frame #2: 0x000000000020a503 vkcube-wayland`demo_create_window(demo=0x00007fffffffd330) at cube.c:2759:27 frame #3: 0x0000000000209ef2 vkcube-wayland`main(argc=1, argv=0x00007fffffffe0e0) at cube.c:3990:5 frame #4: 0x00000000002076ef vkcube-wayland`_start(ap=<unavailable>, cleanup=<unavailable>) at crt1_c.c:75:7