Get rid of cfg_aliases build dependency

[d-e-s-o]

As it turns out cfg_aliases does a borderline trivial thing, in that it basically just checks an environment variable and emits one or two lines of 'cargo:' directives. When a build system other than Cargo is used that does not honor build scripts we end up having to craft similar logic ourselves. In such an instance, all cfg_aliases does is obfuscate what is really going on. So we might as well just include the logic ourselves and get rid of the build dependency, given that we have to do it in one shape or form anyway.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 95.41%. Comparing base (1a4e107) to head (89c73c2). Report is 1 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #876 +/- ## ========================================== + Coverage 95.39% 95.41% +0.02% ========================================== Files 55 55 Lines 10522 10522 ========================================== + Hits 10037 10040 +3 + Misses 485 482 -3 ```

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