Fix double border due to progress guide

[gaearon]

Previously, the progress bar was throwing off the hideTopBorder={index === 0} condition on the top feed item because the progress guide was always getting rendered as a row (even if returning null). To fix this, a couple of things:

• The condition for whether to show the guide has moved into where we create rows rather than in the progress guide component itself.
• I've also removed the top border from the progress guide itself for consistency.

Test Plan

border.mov

Also check it works as expected on mobile web, tablet and desktop (where this widget is in the right pane).

[github-actions]

Old size	New size	Diff
6.78 MB	6.78 MB	127 B (0.00%)

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