Correct a misnomer regarding supplementary code points.

runtime/vm/object_test.cc

Index: runtime/vm/object_test.cc
diff --git a/runtime/vm/object_test.cc b/runtime/vm/object_test.cc
index 8ae0baeacf50b4763f0bf083efc64a44c175f996..86cb9b0bfdcf1a09bd921224a3d9df83e73acca7 100644
--- a/runtime/vm/object_test.cc
+++ b/runtime/vm/object_test.cc
@@ -1312,7 +1312,8 @@ TEST_CASE(StringFromUtf8Literal) {
     }
   }
 
-  // Create a SMP 2-byte string from a UTF-8 string literal.
+  // Create a 2-byte string with supplementary characters from a UTF-8
+  // string literal.
   {
     const char* src =
         "\xF0\x9D\x91\xA0\xF0\x9D\x91\xA1"