[web] Remove last border from My Account page

Summary:
This doesn't match the Figma designs, but discussion on this Linear issue here.

The last border on the My Account page should be removed since there is no border on the top (above Logged in as …).

Before:

After:

Test Plan: Looks as expected on Safari/Chrome.

Reviewers: atul, palys-swm

Reviewed By: atul, palys-swm

Subscribers: ashoat, Adrian

Differential Revision: https://phab.comm.dev/D4280