feat: deprecate MyInfo fields for V3 (step 3 - drop support)

[mantariksh]

To be merged for the release after #1071 and after the scripts in #1072 have been run

Problem

The following MyInfo fields are set to return empty strings, and therefore should be deprecated:

• Home number
• Billing address
• Mailing address
• Highest education level
• School name
• Graduation year

Solution

The deprecation requires 3 steps:

1. Stop allowing admins to add these fields
2. Database migration to convert these fields to regular (non-MyInfo) fields
3. Drop support for these fields

This PR addresses step 3. Here, we remove the deprecated fields from the codebase.

Tests

• Run the following query in production and ensure that you get 0 results: db.getCollection('forms').find({ 'form_fields.myInfo.attr': { $in: ['homeno', 'mailadd', 'billadd', 'gradyear', 'edulevel', 'schoolname']} })
• Submit a form with all MyInfo fields

[mantariksh]

to be merged and released AFTER db scripts have been run