[wasm] Remove obsolete comment

BUG=v8:5766
R=ahaas@chromium.org
NOTRY=true

Review-Url: https://codereview.chromium.org/2622863002
Cr-Commit-Position: refs/heads/master@{#42164}

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

@@ -720,8 +720,6 @@ class WasmRunner : public WasmRunnerBase {
     if (interpret()) return CallInterpreter(p...);
 
     // Use setjmp/longjmp to deal with traps in WebAssembly code.
-    // Make the return value volatile, to give defined semantics if accessed
-    // after setjmp.
     ReturnType return_value = static_cast<ReturnType>(0xdeadbeefdeadbeef);
     static int setjmp_ret;
     setjmp_ret = setjmp(WasmRunnerBase::jump_buffer);