Remove step that copies llvm-symbolizer to the root build dir.

build/sanitizers/BUILD.gn

-# Copyright (c) 2015 The Chromium Authors. All rights reserved.
-# Use of this source code is governed by a BSD-style license that can be
-# found in the LICENSE file.
-
-import("//build/config/clang/clang.gni")
-
-if (is_clang) {
-  copy("copy_llvm_symbolizer") {
-    if (is_win) {
-      sources = [
-        "$clang_base_path/bin/llvm-symbolizer.exe",
-      ]
-      outputs = [
-        "$root_out_dir/llvm-symbolizer.exe",
-      ]
-    } else {
-      sources = [
-        "$clang_base_path/bin/llvm-symbolizer",
-      ]
-      outputs = [
-        "$root_out_dir/llvm-symbolizer",
-      ]
-    }
-  }
-}