fix(placement): adjust hover style for links (#9981)

Top: Both "Mozilla ads" and "Don't want to see ads?" are underlined only on hover.
Sidebar/Footer: "Mozilla ads" is underlined except on hover, and "Don't want to see ads?" is underlined only on hover.

client/src/ui/organisms/placement/index.scss

@@ -47,13 +47,32 @@ section.place {
     }
   }
 
+  &.top .pong-note,
+  .no-pong {
+    text-decoration: none;
+
+    &:focus,
+    &:hover {
+      text-decoration: underline;
+    }
+  }
+
+  &.side .pong-note,
+  &.bottom-banner .pong-note {
+    text-decoration: underline;
+
+    &:focus,
+    &:hover {
+      text-decoration: none;
+    }
+  }
+
   .no-pong {
     color: var(--text-secondary);
     font-size: 0.6rem;
     margin-bottom: 0.5rem;
     max-width: 12rem;
     padding: 0;
-    text-decoration: underline;
     width: 100%;
   }
 
@@ -125,13 +144,6 @@ section.place {
         grid-area: note;
         margin: 0 0 auto auto;
         padding: 0 0.5rem 0.125rem;
-        text-decoration: none;
-
-        &:hover,
-        &:focus,
-        &:active {
-          text-decoration: underline;
-        }
       }
     }
 
@@ -262,7 +274,6 @@ div.empty-place {
       font-size: 0.625rem;
       grid-area: note;
       margin-top: 0.5rem;
-      text-decoration: underline;
     }
 
     .no-pong {