refactor(material/chips): remove unused scss variable

Updates previous changes to remove unused scss variable that I added
for my original solution.

Author: essjay05

src/material/chips/chip.scss

@@ -13,7 +13,6 @@ $_trailing-action-padding: 8px;
 $_avatar-leading-padding: 4px;
 $_avatar-trailing-padding: 8px;
 $_touch-target-size: 48px;
-$_touch-target-vertical-padding: 8px;
 
 $fallbacks: m3-chip.get-tokens();