When navigating to a Sub Flow Run from a Flow Run Details page, the graph doesn't remount.

[brandonreid]

Steps to reproduce:

• View a flow run that contains sub flow runs.
• On the graph, select the sub flow run to view it's details in the side panel.
• Click the flow run graph's name to navigate to it.

Result:
The graph state is stuck rendering the parent flow run.

If you refresh on this page, you'll see the graph render with just the sub flow run nodes.

Expected:
The graph should rerender to show the same state shown on a fresh load.

[pleek91]

Fixed the reactivity issue in prefect-ui-library's FlowRunTimeline component in #1393 but that revealed an issue within the timeline itself where its unable to remove nodes. Closing that PR for now until we can address this more holistically.