Remove deprecated --schema-embed flag from documentation

[lassemoldrup]

Eventually, we should update our developer documentation and remove the deprecated flag from the commands. Just not immediately since most people will still be using older versions of cargo-concordium.

Originally posted by @DOBEN in Concordium/concordium-smart-contract-tools#177 (review)

The --schema-embed flag for cargo-concordium is now default behavior, thus it has been deprecated. There is also now a flag that opts out of embedding called --no-schema-embed that may be worth mentioning in the docs? Either way, references to --schema-embed or -e should be removed from the documentation, when this feature is commonly used.