remove class on preference config modal

[f2cmb]

Description

• It fixes Bad size of Add button in Computers - Select default items to show #21710
• Here is a brief description of what this PR does : removed a class that produce weird behavior of a button.

Before :

After :

Tested in Chrome and Firefox.

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This is better, but all cases are not fixed (see with long column name)

[f2cmb]

New behavior proposal to avoid these problems with long-labelled options :

Desktop :

Mobile :

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This is still not OK with very long labels:

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(see the button is no longer accessible)