Remove tiny data point circles from prerendered graphs

[phieri]

The prerendered graphs on the dashboard currently contains a tiny circle for each datapoint. The circles are so small in the current design that they either are not visible or sort of look like a graphics glitch. This PR removes the circles so that the smooth line is the only shape in the graph.

Reference: https://www.chartjs.org/docs/latest/configuration/elements.html#point-configuration

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[phieri]

@AnandChowdhary Does Koj AG still exist? There's not much purpose in entering into an agreement with a nonexistent counterpart.