stdenv/check-meta: remove onlyLicenses check

[ncfavier]

Fixes #154031. I could not find a reason for this check to exist and @wmertens has not replied. meta.license needs not be an attribute of lib.licenses, so allow/blocklists should not either.

cc @ony @roberth

[wmertens]

So, making sure that the license is a known license is not desirable?

[ncfavier]

The nixpkgs manual says this:

The meta.license attribute should preferably contain a value from lib.licenses defined in nixpkgs/lib/licenses.nix, or in-place license description of the same format if the license is unlikely to be useful in another expression.

In any case, this check isn't ensuring that meta.license is known, only that the block/allowlisted licenses are. The latter would maybe make sense if the former was done, but it's not.

[wmertens]

ah right. 👍 then.

[ncfavier]

@ofborg eval