This test is now pointless and the comment is outdated. Also the test fails
on 32 bit systems with:
../nix_api_value_internal.cc:22: Failure
Expected equality of these values:
sizeof(nix::Value)
Which is: 12
sizeof(nix_value)
Which is: 8
It just happeneded to work because Value is 16 bytes and nix_value was also 16 bytes.
Also get rid of a pointless inline in new_nix_value, since it's already static and
inline there does nothing.
