Revert of Add gclient hook to download prebuilt mojo_shell

mojo/shell/BUILD.gn

Index: mojo/shell/BUILD.gn
diff --git a/mojo/shell/BUILD.gn b/mojo/shell/BUILD.gn
index 54a2fbfecb18a7aabe59ef115ec5e9d30a985d74..ff5f349ddaf203c4bf9892b227175b6a28924b96 100644
--- a/mojo/shell/BUILD.gn
+++ b/mojo/shell/BUILD.gn
@@ -2,13 +2,9 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import("//mojo/public/tools/bindings/mojom.gni")
 import("//build/config/ui.gni")
-import("//mojo/public/mojo.gni")
-import("//mojo/public/tools/bindings/mojom.gni")
-
-if (!use_prebuilt_mojo_shell) {
-
-# GYP version: mojo/mojo.gyp:mojo_shell
+
 executable("mojo_shell") {
   deps = [
     ":lib",
@@ -25,8 +21,6 @@
     "desktop/mojo_main.cc"
   ]
 }
-
-}  # !use_prebuilt_mojo_shell
 
 # GYP version: mojo/mojo.gyp:mojo_shell_lib
 source_set("lib") {