style: Stop setting slider height

Now that the slider requests a correct height, it is no longer
necessary to set it explicitly from the stylesheet.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2994>

data/theme/gnome-shell-sass/widgets/_osd.scss

@@ -23,7 +23,6 @@ $osd_levelbar_height:6px;
     margin-bottom: 4px;
     &:first-child { margin-bottom: 0px; }
 
-    height: $osd_levelbar_height;
     min-width:$base_icon_size * 10;
     -barlevel-height: $osd_levelbar_height;
     -barlevel-background-color: transparentize($osd_fg_color, if($variant=='light', 0.7, 0.9));

data/theme/gnome-shell-sass/widgets/_quick-settings.scss

@@ -84,7 +84,6 @@
 
   .slider-bin {
     &:focus {@include button(focus);}
-    min-height: 16px; // slider size
     padding: $base_padding;
     border-radius: 99px;
   }
@@ -164,10 +163,6 @@
 
 .device-subtitle { color: transparentize($fg_color, 0.5); }
 
-.keyboard-brightness-item .slider {
-  min-height: 16px;
-}
-
 .keyboard-brightness-level {
   spacing: $base_padding;