We would not recommend deleting fields from your custom table(s) but instead would recommend that the field is edited to be hidden. To do this, follow the steps below:
1. Navigate to the Contacts dashboard.
2. Select "Configuration" from the left menu.
3. Choose the "Custom Tables" tile.
4. Hover over the table name listed that contains the field to display the "Edit" button. Click the "Edit" button.
5. Hover over the field listed to display the "Edit" button. Click the "Edit" button.
6. Check the box to hide the field:
7. Click the "Save" button.
Hiding the field will hide it everywhere in the UI other than when viewing the custom table itself in Configuration. You will not be able to see it on the contact profiles or when adding merge tags in your campaigns.