Remove unnecessary get_cancellation_slot().clear() calls

Summary: related to T13706

Reviewers: ivica

Reviewed By: ivica

Subscribers: miljen, iljazovic

Differential Revision: https://repo.mireo.local/D27894

test/include/test_common/delayed_op.hpp

@@ -70,8 +70,6 @@ public:
 
 	template <typename CompletionHandler>
 	void operator()(on_timer, CompletionHandler&& h, error_code ec) {
-		get_cancellation_slot().clear();
-
 		auto bh = std::apply(
 			[h = std::move(h)](auto&&... args) mutable {
 				return asio::append(std::move(h), std::move(args)...);