Clean up button group (#25073)

Clean up button group  (#25073)

* Remove unnecessary float

- since parent btn-group is displayed as inline-flex, the child elements are placed left to right by default.

* Cleanup of reset rounded corners

- Remove `border-radius :0` since it is enough by each reset of left and right side
- A `.dropdown-toggle` selector should not be used for reset rounded corner since it does not have border-radius property. Instead use .dropdown-toggle as negation pseudo-class.