Remove unused props in projects_and_groups_chart and users_chart

The following discussion from !39496 (merged) should be addressed:

• @markrian started a discussion:

  This was surely broken before, right?

  It looks like it didn't matter anyway, since these props aren't used by the component, although they are required.

  I'll open a follow-up issue for this.

Affected files

• spec/frontend/analytics/instance_statistics/components/projects_and_groups_chart_spec.js
• spec/frontend/analytics/instance_statistics/components/users_chart_spec.js
• ~/analytics/instance_statistics/components/projects_and_groups_chart.vue#L28-35
• ~/analytics/instance_statistics/components/users_chart.vue#L19-26
• ~/analytics/instance_statistics/components/app.vue#L27-36