explore better path forward for clippy check failure

[jordanhendricks]

In #1091 there was a clippy check that failed here:

propolis/xtask/src/task_clippy.rs

Lines 46 to 57 in 2c9d705

	// Check the Falcon bits
	//
	// TODO(jph): Currently specifying both the propolis-client and
	// propolis-server packages in a single clippy command will cause clippy
	// to fail because cargo finds 2 copies of propolis-client. This is because
	// dice-util depends on sled-agent-client, which depends on a rev of
	// propolis.
	//
	// We should clean this up by making sled-agent-client not re-export
	// propolis-client..
	failed |= run_clippy(&["--features", "falcon", "-p", "propolis-server"])?;
	failed |= run_clippy(&["-p", "propolis-client"])?;

The less-expedient but more correct solution to fix this is to make propolis-client not re-export propolis-client. Unclear to me how much work that is, but filing for tracking.