[regexp] Remove unused code

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.
 
 import("//build/config/android/config.gni")
 import("//build/config/arm.gni")
 import("//build/config/dcheck_always_on.gni")
 import("//build/config/mips.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 
@@ skipping 392 matching lines @@
   # NOSORT
   sources = [
     "src/js/macros.py",
     "src/messages.h",
     "src/js/prologue.js",
     "src/js/runtime.js",
     "src/js/v8natives.js",
     "src/js/symbol.js",
     "src/js/array.js",
     "src/js/string.js",
-    "src/js/regexp.js",
     "src/js/arraybuffer.js",
     "src/js/typedarray.js",
     "src/js/collection.js",
     "src/js/weak-collection.js",
     "src/js/collection-iterator.js",
     "src/js/promise.js",
     "src/js/messages.js",
     "src/js/templates.js",
     "src/js/spread.js",
     "src/js/proxy.js",
@@ skipping 2556 matching lines @@
   ]
 
   configs = [
     ":external_config",
     ":internal_config_base",
   ]
 }
 
 v8_fuzzer("wasm_data_section_fuzzer") {
 }