* Make sure frame examples compile for wasm

This makes sure that `frame-example` and `frame-example-offchain-worker`
compile for wasm.

This also fixes compilation for these crates. The offchain worker
example doesn't use serde-json anymore as that is too heavy and breaks
`no_std` compilation.

* Apply suggestions from code review

Co-Authored-By: Nikolay Volf <[email protected]>

Co-authored-by: Nikolay Volf <[email protected]>