Removing the select all option in a custom field

[PHenn]

Hello, hopefully this is an easy question to solve. 

I need to add a field on a custom form using the drop down option.  We want the user to be able to select more than one option, but I don't want the option to select "all" to appear.  It seems like the "select all" option is baked into the field.  Is there anyway to remove it?  Or does anyone have a suggested workaround? 

Thank you. 

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[Richard__Carlson]

Have you tried using the checkbox display type?

[PHenn]

Yes, it is frustrating because "all" doesn't show up when you use the preview view in the custom form. It only shows up when you actually use the form. 

[Richard__Carlson]

You're right, it is confusing.

[Leigh_Hasty]

I totally agree and have gotten complaints on that from users.  Here's one on the idea board to upvote:

Remove "all" option for checkbox field