[libc++] LWG3266: delete the to_chars(bool) overload.

This PR only updates the synopsis in `<charconv>` -- the current
implementation already [deletes](https://github.com/llvm/llvm-project/blob/e9e6266c704df43e2c52308e1b653dccefa89e04/libcxx/include/charconv#L108)
the overload and has a [test](https://github.com/llvm/llvm-project/blob/main/libcxx/test/std/utilities/charconv/charconv.to.chars/integral.bool.fail.cpp)
for it (and this has been the case from the first [commit](https://reviews.llvm.org/D41458)
where `<charconv>` was added).

Reviewed By: #libc, Mordante

Differential Revision: https://reviews.llvm.org/D111845