duplicate rules for visibility of class constants

[blue32a]

I think these rules are the same.

• PSR12.Properties.ConstantVisibility (Included in PSR12)
• SlevomatCodingStandard.Classes.ClassConstantVisibility

If it is correct

<rule ref="PSR12">
    <!-- checked by SlevomatCodingStandard.Classes.ClassConstantVisibility -->
    <exclude name="PSR12.Properties.ConstantVisibility"/>
</rule>