[FEA]: Remove unsupported configurations from libcu++

### Is this a duplicate?

- [X] I confirmed there appear to be no [duplicate issues](https://github.com/NVIDIA/cccl/issues) for this request and that I agree to the [Code of Conduct](CODE_OF_CONDUCT.md)

### Component

libcu++

### Is your feature request related to a problem? Please describe.

Due to historical reasons, we have a ton of cruft in the code base. This comes from libc++ supporting compilation modes / platform that we do not support. This includes (not exhausting):

* Conditional `noexcept` support.
* We do not support any standard prior to C++11 so `noexcept` is supported by all compilers we target
* C++03 support
* There is a significant amount of churn around this, as it prevents usage of `using`declarations and variadics
* Unsupported platforms such as SUN / IBM

### Describe the solution you'd like

We should identify unneeded configurations and remove them to reduce code complexity

### Describe alternatives you've considered

We can leave everything as is, as long as we remember why we are doing it.

### Additional context

_No response_