Add contract test: remove_delegate() is a safe no-op when no delegate was ever set

[Austinaminu2]

Description

There's no test confirming that calling `remove_delegate()` on a stream that never had a delegate set doesn't panic or error unexpectedly.

Task

Add a test that calls `remove_delegate()` on a fresh stream with no delegate ever set, and asserts it completes without panicking (and that `get_delegate()` still returns `None` afterward).

Good for contributors because

Small, focused negative-path test addition to the existing delegate test suite.