feat(slider): remove the background that overrides the gradient of the steps (#10357)

* feat(slider): remove the background that overrides the gradient of the steps

* feat(slider): bring back deleted doc param

Co-authored-by: MPopov <[email protected]>
Co-authored-by: Hristo <[email protected]>
Co-authored-by: Simeon Simeonoff <[email protected]>

Author: 4 people

projects/igniteui-angular/src/lib/core/styles/components/slider/_slider-theme.scss

@@ -340,7 +340,6 @@
         width: 100%;
         height: rem($slider-track-height);
         background-size: 100% em($slider-track-height);
-        background-color: --var($theme, 'track-step-color');
         opacity: .85;
         transition: opacity .2s $ease-out-quad;
         z-index: 1;