[libc++][AIX][test] Enable put_double/long_double locale tests

AIX print -0.0 , inf, nan differently, which are causing the test
failures. We are OK for most other tests.

This patch remove the tests related these limitations conditionally on AIX,
so that we can enable the other tests to avoid losing test coverage.

The general direction is:

```
if strings don't differ between environments, keep the string literal "INF" and the padding, instead of folding them into variables.
```

Reviewed By: ldionne, #libc, Mordante

Differential Revision: https://reviews.llvm.org/D120448