Previously, we failed at runtime if an unknown or unstable host function
was called. This requires us to keep track of when a host function was
added and when a code was deployed. We used the `api_version` to track
at which API version each code was deployed. This made sure that when a
new host function was added that old code won't have access to it. This
is necessary as otherwise the behavior of a contract that made calls to
this previously non existent host function would change from "trap" to
"do something".

In this PR we remove the API version. Instead, we statically verify on
upload that no non-existent host function is ever used in the code. This
will allow us to add new host function later without needing to keep
track when they were added.

This simplifies the code and also gives an immediate feedback if unknown
host functions are used.

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Co-authored-by: GitHub Action <action@github.com>