Remove unused string interpolations.

runtime/lib/growable_array.dart

Index: runtime/lib/growable_array.dart
diff --git a/runtime/lib/growable_array.dart b/runtime/lib/growable_array.dart
index ade7ec19e4cf15b6e364955499810a393ef64c78..fd3426ccd95e1507a097c909608601291ddd5177 100644
--- a/runtime/lib/growable_array.dart
+++ b/runtime/lib/growable_array.dart
@@ -262,13 +262,13 @@ class _GrowableList<T> implements List<T> {
     StringBuffer buffer = new StringBuffer();
     if (separator.isEmpty) {
       for (int i = 0; i < this.length; i++) {
-        buffer.write("${this[i]}");
+        buffer.write(this[i]);
       }
     } else {
-      buffer.write("${this[0]}");
+      buffer.write(this[0]);
       for (int i = 1; i < this.length; i++) {
         buffer.write(separator);
-        buffer.write("${this[i]}");
+        buffer.write(this[i]);
       }
     }
     return buffer.toString();