Removing unstable stdlibs + review of diff from latest go version

[thehowl]

https://gnolang.github.io/gno/stdlib_diff/

Ahead of the mainnet launch, we should move into testing stdlibs all standard library packages which are considered unstable, or which lack a significant number of features from Go and would be better to be added in a more "proper" fashion after mainnet, to avoid having to make backward incompatible changes.