Remove unused teal border-top styles

The install card uses the grey code-block variant,
so these teal description border overrides were
never applied.

Author: julioest

static/css/v3/code-block.css

@@ -154,14 +154,6 @@ html.dark .code-block-card--grey {
   border-top: 1px solid var(--color-border);
 }
 
-.code-block-card--teal .code-block-card__description {
-  border-top-color: var(--color-accent-strong-teal);
-}
-
-html.dark .code-block-card--teal .code-block-card__description {
-  border-top-color: var(--color-border);
-}
-
 .code-block__inner {
   display: block;
   margin: 0;