Build fix

Remove the IS_6DOF entry in OpenXR mappings for the khronos simple
profile that was added by mistake. That field existed when the PR
was created but it took so long to review that it was removed in
the meantime.

app/src/openxr/cpp/OpenXRInputMappings.h

@@ -461,7 +461,6 @@ namespace crow {
     // Default fallback: https://github.com/immersive-web/webxr-input-profiles/blob/master/packages/registry/profiles/generic/generic-button.json
     const OpenXRInputMapping KHRSimple {
             "/interaction_profiles/khr/simple_controller",
-            IS_6DOF,
             "generic-trigger.obj",
             "generic-trigger.obj",
             device::UnknownType,