Remove sweeper threads

BUILD.gn

 # 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.
 
 # TODO(jochen): These will need to be user-settable to support standalone V8
 # builds.
 v8_compress_startup_data = "off"
 v8_deprecation_warnings = false
 v8_enable_disassembler = false
 v8_enable_gdbjit = false
@@ skipping 658 matching lines @@
     "src/heap/mark-compact.h",
     "src/heap/objects-visiting-inl.h",
     "src/heap/objects-visiting.cc",
     "src/heap/objects-visiting.h",
     "src/heap/spaces-inl.h",
     "src/heap/spaces.cc",
     "src/heap/spaces.h",
     "src/heap/store-buffer-inl.h",
     "src/heap/store-buffer.cc",
     "src/heap/store-buffer.h",
-    "src/heap/sweeper-thread.h",
-    "src/heap/sweeper-thread.cc",
     "src/hydrogen-alias-analysis.h",
     "src/hydrogen-bce.cc",
     "src/hydrogen-bce.h",
     "src/hydrogen-bch.cc",
     "src/hydrogen-bch.h",
     "src/hydrogen-canonicalize.cc",
     "src/hydrogen-canonicalize.h",
     "src/hydrogen-check-elimination.cc",
     "src/hydrogen-check-elimination.h",
     "src/hydrogen-dce.cc",
@@ skipping 732 matching lines @@
     deps = [
       ":v8_base",
       ":v8_nosnapshot",
     ]
   }
 
   direct_dependent_configs = [ ":external_config" ]
 }
 
 }