Delete silk_flags.py

It doesn't appear to be used anywhere and some of the flags it adds no
longer exist.

Fixed: 1133368
Change-Id: I32833b330ca574b18dc0ca5e457ab9acbe0ab333
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2450329
Commit-Queue: Wenbin Zhang <wenbinzhang@google.com>
Reviewed-by: Wenbin Zhang <wenbinzhang@google.com>
Auto-Submit: kylechar <kylechar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#815925}

tools/perf/benchmarks/silk_flags.py

-# Copyright 2014 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.
-
-
-def CustomizeBrowserOptionsForSoftwareRasterization(options):
-  """Enables flags needed for forced software rasterization."""
-  options.AppendExtraBrowserArgs('--disable-gpu-rasterization')
-
-
-def CustomizeBrowserOptionsForGpuRasterization(options):
-  """Enables flags needed for forced GPU rasterization using Ganesh."""
-  options.AppendExtraBrowserArgs('--force-gpu-rasterization')
-
-
-def CustomizeBrowserOptionsForSyncScrolling(options):
-  """Enables flags needed for synchronous (main thread) scrolling."""
-  options.AppendExtraBrowserArgs('--disable-threaded-scrolling')
-
-def CustomizeBrowserOptionsForThreadTimes(options):
-  """Disables options known to cause noise in thread times"""
-  # Remove once crbug.com/621128 is fixed.
-  options.AppendExtraBrowserArgs('--disable-top-sites')