Drop support for AssemblyScript and Go contracts

[ppedziwiatr]

We're dropping support for the Go and Assemblyscript in the SDK (zero interest in the community + some technical issues with both technologies).

Issues w AssemblyScript:

• no support for async, without using some additional processing (https://kripken.github.io/blog/wasm/2019/07/16/asyncify.html)
• the language itself is lacking in terms of features (i.e. no closures support)

Issues with Go:

• very big bundle size with default compiler (3MB for hello world)
• with tinygo compiler - the hello world has ~300kB, but is lacking support for JSON ser/de (some weird, 3rd libs needs to be used)
• very weird and non standard way of 'glueing' wasm code with the host (e.g. no standard module.export functions)

[ppedziwiatr]

Removed in 1.2.52