fix(multiple): fix density prefixes

Author: Andrew Seguin

src/material/core/tokens/_density.scss

@@ -101,7 +101,6 @@ $_density-tokens: (
       arrow-transform: (translateY(-8px), translateY(-8px), none),
     ),
     (mat, sidenav): (),
-    (mat, slide-toggle): (),
     (mat, slider): (),
     (mat, snack-bar): (),
     (mat, sort): (),