Checkbox labels should not be hidden in inline forms

[BBoom]

Q	A
Is bugfix?	✔️
New feature?	❌
Breaks BC?	❌
Fixed issues

Note: This is the same issue fixed in https://github.com/yiisoft/yii2-bootstrap4/pull/243 for bootstrap 4.

-- Inline forms by default hide all labels with the sr-only class. This should not happen for checkbox elements, which need their label to function. Without a visible label, the checkbox will not function in bootstrap. And even if it did, a checkbox without a label is not really usable.

The method for class removal is based on similar exceptions made in the listBox() and dropDownList() methods in the same class.