Remove libc++abi dependency on mac

BUG=729032
R=jshin@chromium.org

Review-Url: https://codereview.chromium.org/2921843003 .
diff --git a/BUILD.gn b/BUILD.gn
index 20ade24..76914cd 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -945,10 +945,6 @@
     ":icudata",
   ]
 
-  if (is_mac && using_sanitizer) {
-    deps += [ "//buildtools/third_party/libc++abi" ]
-  }
-
   configs -= [
     "//build/config/compiler:no_rtti",  # ICU uses RTTI.
     "//build/config/compiler:chromium_code",