use region landmark for cells

[tonyfast]

a conversation in a11y slack made indicated that the form is being used as an anchor, not a landmark. this change:

• makes the cell an explicit region while maintaining the feed pattern
• removes the form label

[tonyfast]

this approach with be more reliable across screen readers, and what i was doing before was inconsistent

ref: https://www.scottohara.me/blog/2019/04/05/landmarks-exposed.html