Cleanup compilation of static binaries

Context

We no longer use the env stanza because its scope is too wide. We want precise control of what binaries should be compiled in static mode. Also remove ~static_cclibs from the manifest as it's unused and it allows to simplify the manifest quite a bit.

External dune PR https://github.com/ocaml/dune/pull/5215

Based on !3976 (merged) and !3958 (merged)

Dune 3 will allow us make static compilation of binary much less invasive in dune files

Manually testing the MR

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
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• Provide automatic testing (see the testing guide).
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