gn: Remove unused bind.h include from run_all_unittests.cc

BUG=None
TEST=ninja -C out/Debug gn_unittests
TBR=brettw@chromium.org

Review URL: https://codereview.chromium.org/583453003

Cr-Commit-Position: refs/heads/master@{#295853}

tools/gn/run_all_unittests.cc

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "base/bind.h"
 #include "base/test/test_suite.h"
 
 // Don't use the multiprocess test harness. This test suite is fast enough and