[morley-debugger#2] Fix cast not removing annotations

Description

Problem: CAST currently doesn't remove annotations, creating a stack element that still has them.

Solution: Discard notes in interpreter, recreating the value without notes. Note that variable annotations are still preserved, and running tezos-client typecheck script indeed preserves them, which indicates correct behavior.

Related issue(s)

Resolves morley-debugger#2 (closed)

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