Remove unused include of wtf/atomics.h in idb_database.cc.

Change-Id: Ic5f75f1cabac1adecbf0158d3a508eaec876da02
Reviewed-on: https://chromium-review.googlesource.com/c/1348856
Commit-Queue: Victor Costan <pwnall@chromium.org>
Reviewed-by: Victor Costan <pwnall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#610495}

third_party/blink/renderer/modules/indexeddb/idb_database.cc

@@ -49,7 +49,6 @@
 #include "third_party/blink/renderer/platform/bindings/exception_state.h"
 #include "third_party/blink/renderer/platform/histogram.h"
 #include "third_party/blink/renderer/platform/wtf/assertions.h"
-#include "third_party/blink/renderer/platform/wtf/atomics.h"
 #include "third_party/blink/renderer/platform/wtf/std_lib_extras.h"
 
 #include <limits>