Remove TODO comments about spacing variables (#10695)

The variables on _spacing.pcss have been deprecated by https://github.com/matrix-org/matrix-react-sdk/pull/10686

res/css/views/messages/_EventTileBubble.pcss

@@ -15,10 +15,10 @@ limitations under the License.
 */
 
 .mx_EventTileBubble {
-    --EventTileBubble_margin-block: 10px; /* TODO: Use a spacing variable */
+    --EventTileBubble_margin-block: 10px;
 
     background-color: $dark-panel-bg-color;
-    padding: 10px; /* TODO: Use a spacing variable */
+    padding: 10px;
     border-radius: 8px;
     /* Reserve space for external timestamps, but also cap the width */
     max-width: min(calc(100% - 2 * var(--MessageTimestamp-width)), 600px);