Removes borders on Usage Quotas Seats details table

What does this MR do and why?

Removes extra borders from the access details table on Usage Quotas > Seats tab.

Also it:

• aligns members rows and details rows horizontally
• makes the details expand button bigger (was 16x32, now 32x32), thus easier to click
• aligns members avatars vertically for members with and without access details (expand button)

Fixes #376701 (closed)

Screenshots or screen recordings

	Before	After
single entry in details
multiple entries

How to set up and validate locally

1. Open a Namespace Usage Quotas > Seats tab (e.g.: http://localhost:3000/groups/h5bp/-/usage_quotas#seats-quota-tab)

2. Expand details on a user and see the details below the user row

NOTE: If there's too few data entries — one can invite members to a group (http://localhost:3000/groups/h5bp/-/group_members) or to a project (http://localhost:3000/h5bp/html5-boilerplate/-/project_members).

MR acceptance checklist

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