Remove formstacks and references to forms from LATAC

[shakao]

[sc-11273]

• removes formstacks from the landing page
• removes references to forms from My letters page
• small CSS tweaks to homepage
• small copy changes (pending confirmation + localization, getting this up on the demo site for now and will make copy changes later if any come through)

Mobile:

Desktop:

[shortcut-integration[bot]]

This pull request has been linked to Shortcut Story #11273: Remove Formstacks from LA TAC.