It is not possible to have a constant-initialized object of type
absl::NoDestructor<T>. Fix the documentation so that it doesn't
mention this possibility. Only recommend it use as a function-scope
static variable, and discourage its use as a global variable.
PiperOrigin-RevId: 647488395
Change-Id: Ifee052fce07609d3de72cddc30e86de67706cd91
