[wasm] Drop unused variables in asm-types-unittest.

BUG= https://bugs.chromium.org/p/v8/issues/detail?id=4203
TEST= cctest/asmjs/test-asm-typer
LOG=N
R=jpp@chromium.org

Review-Url: https://codereview.chromium.org/2147113002
Cr-Commit-Position: refs/heads/master@{#37733}

test/unittests/wasm/asm-types-unittest.cc

@@ -266,8 +266,8 @@ TEST_F(AsmTypeTest, IsExactly) {
 }
 
 bool FunctionsWithSameSignature(AsmType* a, AsmType* b) {
-  if (auto* func_a = a->AsFunctionType()) {
-    if (auto* func_b = b->AsFunctionType()) {
+  if (a->AsFunctionType()) {
+    if (b->AsFunctionType()) {
       return a->IsA(b);
     }
   }