[wasm] Refactor encoder.h to use a proper buffer and remove OldFunctions section.

test/cctest/wasm/wasm-run-utils.h

Index: test/cctest/wasm/wasm-run-utils.h
diff --git a/test/cctest/wasm/wasm-run-utils.h b/test/cctest/wasm/wasm-run-utils.h
index 4bbbac326d406d27214e4636a6a304f1a8a6a353..8aa8cff940d050a7aff1ead5d5367569bcae970c 100644
--- a/test/cctest/wasm/wasm-run-utils.h
+++ b/test/cctest/wasm/wasm-run-utils.h
@@ -179,7 +179,7 @@ class TestingModule : public ModuleEnv {
       module_.functions.reserve(kMaxFunctions);
     }
     uint32_t index = static_cast<uint32_t>(module->functions.size());
-    module_.functions.push_back({sig, index, 0, 0, 0, 0, 0, false});
+    module_.functions.push_back({sig, index, 0, 0, 0, 0, 0});
     instance->function_code.push_back(code);
     if (interpreter_) {
       const WasmFunction* function = &module->functions.back();