Remove the on-hover expansion of the downstream pipelines

🧩 Problem

In !66274 (merged) we added the downstream pipeline visualization to the mini pipeline graph. The downstream pipeline can be difficult to interact with when the width of the container isn't enough to expand the graph on hover without wrapping it to a new line. When the wrapping happens, the graph jumps and makes it difficult to click on the right stage in the pipeline.

Screen_Recording_2021-07-20_at_15.38.35

🎨 Proposal

Remove the on-hover expansion of the downstream pipelines.

The downstream pipeline buttons will appear next to each other with the same space in-between as in the main mini-pipeline graph.