Use cargo-run-bin, remove soroban-cli install from just setup

[chadoh]

This project already depends on a certain version of stellar-cli (fka soroban-cli) in (various of) its Cargo.toml file(s). It also installs a pinned version of it using just setup (check the Justfile). This just setup is what we rely on in CI to get the correct version installed.

Let's instead use cargo-run-bin, so we don't need to keep these two versions in-sync.