solana: cleanup: Use assert consistently in src/instructions/mod.rs

[johnsaigle]

          @kcsongor I think you can delete this `assert` as well given the behaviour of `try_release`. It looks a bit funny to have it in one path/mode but not the other. I think we should do both or neither.

It can be done in a separate cleanup PR though. We don't need to derail this PR.

Originally posted by @johnsaigle in #404 (comment)