Remove non-functional "Custom" option from MathCAT decimal separator (#20613)
Closes #20425
Summary of the issue:
In the Math settings panel, the "Decimal separator for numbers" setting offered a "Custom" option that did nothing; the suggested solution was to remove the option.
Description of user facing changes:
Removed the non-functional "Custom" choice from the "Decimal separator for numbers" combo box in Math settings. The remaining choices are Automatic, "." and ",".
Description of developer facing changes:
None
Description of development approach:
hide custom as an option when rendering the control