Do not use new struct type where unnecessary.

test/cctest/interpreter/bytecode_expectations/ForIn.golden

Index: test/cctest/interpreter/bytecode_expectations/ForIn.golden
diff --git a/test/cctest/interpreter/bytecode_expectations/ForIn.golden b/test/cctest/interpreter/bytecode_expectations/ForIn.golden
index 4acc95246eff033a7ee9b0d5c52c7ce30cdc282e..4c2984dbc2cf21bf2ce96497a73552fcf562ddc6 100644
--- a/test/cctest/interpreter/bytecode_expectations/ForIn.golden
+++ b/test/cctest/interpreter/bytecode_expectations/ForIn.golden
@@ -132,7 +132,7 @@ bytecodes: [
   /*   80 S> */ B(Return),
 ]
 constant pool: [
-  CONSTANT_ELEMENTS_PAIR_TYPE,
+  TUPLE2_TYPE,
 ]
 handlers: [
 ]
@@ -189,7 +189,7 @@ bytecodes: [
 ]
 constant pool: [
   FIXED_ARRAY_TYPE,
-  CONSTANT_ELEMENTS_PAIR_TYPE,
+  TUPLE2_TYPE,
   ONE_BYTE_INTERNALIZED_STRING_TYPE ["a"],
 ]
 handlers: [
@@ -234,8 +234,8 @@ bytecodes: [
   /*   98 S> */ B(Return),
 ]
 constant pool: [
-  CONSTANT_ELEMENTS_PAIR_TYPE,
-  CONSTANT_ELEMENTS_PAIR_TYPE,
+  TUPLE2_TYPE,
+  TUPLE2_TYPE,
 ]
 handlers: [
 ]