Remove unused symbol in mark-compact.h

Change-Id: I2992b0db7f403f682032f9b427c1f8c5238cf61e
Reviewed-on: https://chromium-review.googlesource.com/1205290Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55659}

AUTHORS

@@ -162,6 +162,7 @@ Vladimir Krivosheev <develar@gmail.com>
 Vladimir Shutoff <vovan@shutoff.ru>
 Wiktor Garbacz <wiktor.garbacz@gmail.com>
 Xiaoyin Liu <xiaoyin.l@outlook.com>
+Yannic Bonenberger <contact@yannic-bonenberger.com>
 Yong Wang <ccyongwang@tencent.com>
 Yu Yin <xwafish@gmail.com>
 Zac Hansen <xaxxon@gmail.com>

src/heap/mark-compact.h

@@ -500,8 +500,8 @@ class MarkCompactCollector final : public MarkCompactCollectorBase {
     }
 
     HeapObject* PopBailout() {
-      HeapObject* result;
 #ifdef V8_CONCURRENT_MARKING
+      HeapObject* result;
       if (bailout_.Pop(kMainThread, &result)) return result;
 #endif
       return nullptr;