Executor: Remove `LegacyInstanceReuse` strategy (#1486)

It seems the old strategy have been depracted more than one year. 
So maybe it's time to clean up old strategy for wasm executor.


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polkadot address: 15ouFh2SHpGbHtDPsJ6cXQfes9Cx1gEFnJJsJVqPGzBSTudr

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Co-authored-by: Bastian Köcher <[email protected]>
Co-authored-by: Koute <[email protected]>