Remove som GYP annotations, remove unused manifest.

gpu/tools/compositor_model_bench/BUILD.gn

 # Copyright 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/ui.gni")
 
 if (is_linux && !is_chromeos && current_cpu != "arm" && use_x11) {
-  # GYP version: //gpu/tools/tools.gyp:compositor_model_bench
   executable("compositor_model_bench") {
     sources = [
       "compositor_model_bench.cc",
       "forward_render_model.cc",
       "render_model_utils.cc",
       "render_models.cc",
       "render_tree.cc",
       "shaders.cc",
     ]
 
     libs = [ "GL" ]
 
     configs += [ "//build/config/linux:x11" ]
 
     deps = [
       "//base",
       "//build/config/sanitizers:deps",
       "//ui/gl",
       "//ui/gl/init",
     ]
   }
 }