docs(Grid): remove $

Author: MPopov

projects/igniteui-angular/src/lib/core/styles/themes/schemas/light/_grid.scss

@@ -12,7 +12,7 @@
 /// @prop {Map} header-background [igx-color: ('grays', 100), hexrgba: #fff] - The table header background color.
 /// @prop {Map} header-text-color [igx-color: ('grays', 600)] - The table header text color.
 ///
-/// @prop {Map} $sorted-header-icon-color [igx-color: ('secondary', 500)] - The sorted table header icon color.
+/// @prop {Map} sorted-header-icon-color [igx-color: ('secondary', 500)] - The sorted table header icon color.
 /// @prop {Map} sortable-header-icon-hover-color [igx-color: ('secondary', 500)] - The icon color on hover in grid header when the column is sortable.
 ///
 /// @prop {Number} header-border-width [1px] - The border width used for header borders.