Investigate the ways to eliminate the need of getTimelineHeight selector

This was come up during the review of #2549. Currently, we are using `getTimelineHeight` function to determine the height of the tracks. But it's pretty messy because there are a lot of combinations right now. We should try to see if we can come up with a better solution here. It would be great if we can remove this function and statically use the values we calculated.

┆Issue is synchronized with this [Jira Task](https://mozilla-hub.atlassian.net/browse/FP-266)