[Slider] Center the value label (#19330)

Author: Lorenz Henk

packages/material-ui/src/Slider/ValueLabel.js

@@ -20,7 +20,6 @@ const styles = theme => ({
       duration: theme.transitions.duration.shortest,
     }),
     top: -34,
-    left: 'calc(-50% + -4px)',
     transformOrigin: 'bottom center',
     transform: 'scale(0)',
     position: 'absolute',