Pure dead-code cleanup in contracts/stream_contract. Two self-contained fixes, one commit each. No logic changes, no test changes.

Fix 1 — Remove duplicate if stream.paused guard in withdraw

Fixes #534

The withdraw function had two back-to-back identical guards:

// Before
Self::validate_stream_active(&stream)?;
if stream.paused {
    return Err(StreamError::StreamInactive);
}
if stream.paused {          // ← dead code, never reached
    return Err(StreamError::StreamInactive);
}

Because the first if stream.paused block always returns early when true, the second block was unreachable. It was removed, leaving the single correct check in place.

Impact: No behaviour change. Reduces compiled WASM size by 3 lines of redundant bytecode. Eliminates reader confusion.

Fix 2 — Delete orphaned contracts/stream_contract/src/stream_contract/ subtree

Deleted: contracts/stream_contract/src/stream_contract/src/test.rs (61 lines)

Fixes #535

A nested stream_contract/src/ directory existed inside the real src/. lib.rs declares mod test;, which Rust resolves to src/test.rs (the 2 349-line real suite) — the nested path is never on the module search path and was therefore never compiled or run.

The 61-line file contained a single fuzz_stream_invariants test exercising four arithmetic invariants. All four are already covered by dedicated tests in the real src/test.rs:

Impact: No test coverage lost. Removes confusing dead directory from code navigation and search results.

Checklist

• Dead duplicate if stream.paused block removed from withdraw
• Orphaned contracts/stream_contract/src/stream_contract/ directory deleted
• No logic or semantic changes made
• cargo test scope unaffected (only dead code removed)
• Each fix is an isolated, atomic commit