v1 recipe should iniciate that the old selector method isn't valid

[raybellwaves]

Solution to issue cannot be found in the documentation.

• I checked the documentation.

Issue

If a v1 recipe has selectors like # [unix] then it say please use the selector method required for these such as if else statements (https://rattler.build/latest/selectors/#selectors-in-recipes).

For example, it spend me a couple days to work out this in conda-forge/staged-recipes#28437

Installed packages

NA

Environment info

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